I disagree that the government would be a significant issue in a world where lobbyists are a thing. Buying the necessary parts of the government becomes trivial: your lobbyists give them free immortality in return for passing whatever laws you want. No other lobbyists can ever outbid you. See: Disney and copyright.
"What would stop such company from just making new currency of "hours", "days", "months", "years", "decades" and so on, and making everyone want to work for them?"
Well, I'd argue that at least amongst the people I know, close to everyone wants to work for a computer games company. The problem is manifold, but includes:
1) There just aren't that many jobs available for your desired company, whatever that company is.
2) If everyone did work for that company... what would be the point, in anything? You'd have, effectively, a combination of a socialist society and a meritocracy. Everyone works for the Big Company, and gets paid according to their worth to the company. That payment is then exchanged at company stores, for other company products. Suddenly, as well as life extension, the company is having to manufacture and provide hair extensions, hamburgers, USB chargers... and if there are no other companies, then they can't outsource it to anyone. Who wants to rule the world, if you have to then run every childcare, every hair salon, every sewerage plant...
So, even the world's most wealthy company, even if it diversified and bought out most other companies, is very unlikely to make everyone work for it, or even to want to. Typically, a company wants fewer employees in order to reduce overheads.
"Total costs of a year of youth is significantly less than one man-year. For example, total of ten man hours to produce equipment, maintenance, energy and all for a year of lifespan granted."
This paragraph is confusing: I suspect you mean "significantly more" - that is, as you describe, the cost to buy an extra year, is ten years' work for the average man-in-the-street, rather than the other way around. But let's investigate both.
10x more than average US wage. You've then put a price on an extra year of life at about $450k in today's money. Meaning, the average man can't typically get much of an extension and is better off just living well; but anyone rich enough to afford to hire ten flunkies to sit around and do nothing, can also afford immortality. So, the elite become immortal, but this affects everyday life of normal people only through the laws that the company gets pushed through to protect its intellectual property, and through the job opportunities offered for rejuvenating the rich. For each person rejuvenated for a year, ten people get paying jobs. Yay for the economy!
1/10 average US wage. You've then put a price on an extra year of life at about $4.5k in today's money. This is where it gets interesting, because youth drops within the reach of common men. The average man can remain alive indefinitely for what is essentially a 10% tax. The poor are shortlived and a vast class divide opens up between the middle-class and lower-class. For the have-nots, crime can actually pay: even if you get caught, you just need to earn enough to cover your time in jail, plus 10%. Jails become even more crowded.
Punishment: there'd be the new punishment of getting banned from the rejuvenation system, or having limits imposed (you can only rejuvenate between this range of physical ages, etc), and the crimes for which you can be punished in this way are whatever the Company decides. Don't make your debt repayment to them? Publish a blog post defaming them? sky's the limit, there's no law saying they have to serve you.
Perversion: The pedo contingent moves from online chatrooms into reality, of course, along with the ABDLers and neotenists and others, as cliques of eternal children, and those who prey on them, protect them, and service their needs. Age-discrimination laws might change - would someone ten years old physically be subject to the same laws as someone mentally ten years old? And yet, this stops being a big deal - with so many youthful-seeming people with power, instead, the big deal becomes those who fetishize and prey upon the vulnerable aged, with their lowered faculties, technological inexperience, and so forth.
Population: The population... does it explode? Probably not. Nobody actually dies of "old age", even now, so by reversing aging, you have just removed the damage that time has done to their person. Perhaps this treatment also reverses the course of those many common age-related chronic ailments, like cancer, diabetes, hypertension, heart disease, liver disease, Alzheimers, etc that 50% of people over 65 currently have at least two of? This might affect death rates, then. But I doubt population would explode too violently. People would still die, of the same causes, disease, accident, war, murder, suicide and more.
Illness: And, knowing that the Treatment would reverse the ailments, people would take greater risks. The Treatment fixes up livers and lungs? Well, let's smoke and drink! It fixes AIDS? Well, then sex is safe again, and we can carry once more down the path of libertinage that the 60s and 70s went down before AIDS reared its ugly head!
Children: People might not live forever, but they live a lot longer... but they don't have such a rush to have kids. Maybe they'll wait until after their first rejuve. Or the tenth. When the time is right. When they've got a bit more money, and can afford to get a house for the kids as well as an education. Because, inheritance largely dies out. Each new generation needs to buy its own home, and so forth. Retirement funds and pensions would be a thing of the past, eaten up by the rejuvenation process.
Immigration: In the shrinking-population US, immigration is OK, but in the rising-population post-rejuve society, immigration becomes a danger to you and your children. House prices, education, and so much more will become more expensive. So immigration will be discouraged... UNLESS there are laws allowing immigration of the can't-rejuves, to do the "poor people" jobs, and by providing the "poor part" of the population, hence ensure that it is much harder for full citizens to fall down to the can't-rejuve level. Social upward mobility from the can't-rejuves into the rejuvables would be strongly discouraged by the wealthy, though there'll always be rights activists who fight for equality.
Debt: Death is no longer the solution to all life's ills: you can't run up all your cards and shrug, saying "well, I'll be dead soon anyway". But just as today's healthcare debt burden is bad, so the rejuvenation debt burden will be crippling for many. Eventually, they will be unable to afford another rejuve, and as their bodies fail, they'll be less and less able to earn, so less and less able to rejuve. There'd be charities for such hopeless cases, and rejuve lotteries, but the vast majority will age and die.
ID Cards: Identity will be harder to prove, and so biometrics will matter more: a DNA pinprick to prove that you really are yourself, and not your granddaughter.
SOME of these effects would still happen with crazily expensive rejuvenation... but not nearly as much social upheaval as if the common man could attain immortality.