Lead - Lithium = Gold?
Assuming that the method uses Lead-208, transmuting that into Gold produces Lithium-11 which almost immediately decays into Beryllium-11. Beryllium is useful as an alloy in nickel or copper. The market for beryllium isn't very large but appears to be growing and was sold for $230/pound in 2010. This inventor is going to have to be careful because powdered beryllium is carcinogenic.
Mine no more
Before this invention there was only one way to acquire gold, to dig it up or pan for it in rivers. Gold mining operations are expensive, dangerous and ecological destructive. Access to certain gold deposits is only feasible when the price of gold is above a certain price. (No one mines gold for fun, only profit.) According to this graph, the cost of mining gold in North America is \$580/oz. In a mine in South Africa, it costs \$1519/oz. Most mines cost about \$1100 to \$1300 (USD) per ounce of gold mined. Any time the cost of gold is less than these costs, the mining company takes a loss. (Gold miners are well known for using less clear accounting methods to calculate mining costs.)
This guy has created a disruptive innovation in the gold mining industry. A normally extremely expensive material has suddenly become very cheap and easy to create. Lead makes up 0.00099% of the earth's crust. Gold makes up 3.1×10^-7 %.
As of this writing, lead costs about \$0.77 per pound or \$0.05 per ounce. Let's assume \$1100/oz for gold. Since the cost of electricity is 1/30th the increase in value, leading to $36 dollars in electricity for each ounce of gold produced. At 10 cents per kilowatt hour, this is 36,000 kilowatt hours per ounce produced. In order to keep up this kind of power draw, he would need to be buy power on industrial contracts and build an actual factory to make it. For comparison, the average US household consumes about 1000 kilowatt hours per month. Let's assume \$20 in consumables and equipment costs.
Total cost for one ounce of "artificial gold" is \$36+\$.05+\$20=\$56.05. Even so, this kind of gold production is ridiculously cheap by an order of magnitude.
Effects on the Gold Market
Let's measure this in terms of the spread of knowledge and quantity available.
Inventor + 0 and first Ounce - The inventor is able to sell this for \$1100/oz and starts to payback his research and equipment costs. The larger gold market doesn't even know it's dead yet. Selling one ounce amounts to statistical noise in the market. He verifies his own samples using 'aqua regia'.
Inventor + 0 and first 1000 Ounces - The inventor has recovered his costs and wants to show proof of his invention to his friends. Gemologists and metals experts are loaned samples to verify his method but are not told where the gold came from. The inventor is now a millionaire. Our inventor has hired a security force and started construction on a high security gold factory because the power requirements for larger gold production is greater than available at the Inventor's residence.
Inventor + 2 and first 2000 Ounces - Metals experts report the unusually high quality of the gold and verify it's authenticity. The inventor has told two of his friends and they have duplicated his results. Metals experts verify their samples are also sound. The US gold market varies between 100,000 oz and 400,000 oz per day so spreading 2000oz of gold over a month goes unnoticed. Spreading out the gold sales over a monthly period prevent huge moves in the market and helps conceal the price advantage the inventor+friends enjoy. Inventor+friends will also need to find a way to deliver their gold because anyone who has no previous dealings in gold but suddenly starts supplying non-trivial quantities is going to come under suspicion.
Inventor + 10 and the first 10,000 ounces - Secrecy is paramount because a leak at this point could draw the attention of very powerful, well-backed interests, namely the Mob, every single terrorist organization and every government on the planet. No patents are filed with the US Patent Office or any international patent organizations. The Inventor and his friends spend all their time at the factory. They definitely have gold fever.
Inventor + 25 and the first 50,000 ounces - The market has noticed an influx of supply from an unknown source and started to ask questions. Talking heads assume that old pensioners are dumping their stocks or the Fed is doing something crazy....and get it all wrong. The cost of gold drops slightly on increased supply. The gold factory is in full swing but lead supplies are unaffected. The US government start to go looking for the source of this new gold supply.
Inventor + 50 and the first 100,000 ounces - The first rumors of an alchemist who makes gold from lead hit the broader markets. Many don't believe it, after all, alchemists in Europe in the Middle Ages tried and failed. The beryllium market sees an unexpected but significant increase in supply. The cost of gold continues a slow slide on increased supply. The Feds are still looking and starting to close in.
Inventor + 100 and the first 150,000 ounces - In order to avoid being captured, the Inventor breaks the story on international news that he has found a way to transmute lead into gold. After the initial interview, he sequesters himself in his factory and grants no more interviews. However, his friends and friends of friends explain the method. The metals experts referenced earlier will verify that the gold is real. The cost of gold drops like a stone because of supply shock and a loss of confidence. Shares of gold mining companies drop even more dramatically as stock holders attempt to exit a now dead industry by selling their stock. The broader stock market goes into a brief chaos mode as the news is digested.
The broader economy doesn't change much since gold, while valuable, wasn't used in a huge number of places. (Compared to a drop in oil price, gold just doesn't have the same kind of impact.) Large investment institutions like pension funds may hold a lot of gold but are also incredibly diversified so the impact is minimal. Investors who have specialized in holding gold will take a huge hit, losing 90% of their investment though this kind of investor is, hopefully, rare as every single investment strategy ever recommends diversification to guard against just this kind of devaluation.
Inventor + 10,000 and the first 1,000,000 ounces - Manufacturers pile into the market once they know the method. Everyone attempts to get into the gold market while the price still reflects the old scarcity. In a few short months after the new factories go up, gold becomes a normal commodity and floats at around \$100/oz reflecting the cost of lead and electricity plus markup. Gold is no longer the investment of last resort. Banks and governments move to platinum, silver, or palladium as a reserve metal thus forcing the cost of those metals higher.
Goldbugs have a crisis of identity as the metal they have staked so much of their identity on is now cheap and common.
While sanction evasion using gold is still useful, it doesn't pack the same price/weight ratio it once did. Platinum and palladium take over the role of sanction evasion.
Engineers the world over rejoice. Many of them are aware of instances where gold is the perfect material for a specific implementation but had to choose a different material because gold was so expensive previously. All electrical cable plugs can now be gold plated instead of just the expensive ones. Silverware manufacturers can now expand their product lines with solid gold wares instead of just silver or stainless steel. Dentists see a marked increase in gold crowns instead of porcelain.
In some circumstances, gold replaces copper. PC case modders go on a kick of making gold cases because why not? It's gold!
While gold isn't yet cheap enough to use as the cores of network cables, it does find its way into extremely high end audio cables for audiophiles. They praise the round golden tones, superior conductivity and minimal noise of the new cables. Everyone else continues to make fun of them for it.
Gold jewelry sees a huge increase in demand. It's still a beautiful metal and the previous price barrier that prevented more people from owning gold jewelry has disappeared. This demand for jewelry helps prop up demand at the new low price range. Gold is still more expensive than silver's \$20/oz.
Other inventors look for ways to extend the lead-to-gold technique to other metals. The search continues.
Fort Knox becomes a museum to a by-gone era.
Granted, this Inventor is a much cooler customer than James W. Marshall who discovered gold at Sutter's Mill in the California Gold Rush.