It depends on how long your civilization has had time travel, and whether or not there are restrictions on traveling to time periods prior to the advent of the time machine. There are a few things to consider here for dealing with typical materials.
Ruining the Future
Let's say that time machines themselves are an in-demand commodity, and a major raw material which is needful to create time machines is (just an example) erbium. Erbium is rare, but necessary for everyone's expected quality of life (because it's a component in time machines), so it maintains a state of high-demand.
Erbium is hard to come across, but was relatively inexpensive at the time people were just beginning to gather and refine it into time-machine grade metals. If someone were to go back to the time just before time-machines were popularized, they could gather a large quantity of the material for little cost, but they would risk disrupting the advent of time machines themselves (and without time machines, erbium isn't so valuable anymore). Thus, while harvesting Erbium from other time periods may be legal, it is only profitable to take Erbium from times after a certain date.
Now, each time period will desire a certain supply of the material in order to manufacture their goods. Knowing that, different periods in time may desire to prevent the future from harvesting their Erbium. If one goes to the past and takes Erbium from the ground in the year 3042, they prevent a business which otherwise would have acquired the same Erbium in 3058, and so that other business will instead send its time travelers to 3035. In response, you send your miners even farther into the past, until you reach the legal limit. So, all past-harvesting operations must default to the earliest time period allowable.
In addition, in order to prevent actions which would cause society to fail to develop properly, harvesting operations in the past must only take materials which would have otherwise remained untapped or undiscovered until the origin date for the operation. For example, suppose I live in the year 5600 and I discover an untapped Erbium mine in my back yard. It's unbelievable nobody noticed this before. I want to mine it, and I want to secure my investment from time-leap-frogging. So, I invest in some gear and send it to the profit-time-wall and begin harvesting then. This means that the quantity of a material available at any time is still limited to what you can find that wasn't already tapped. So, mining from the past doesn't reduce the value of a material.
In a real way, the market could easily be flooded by taking tons and tons of erbium from the future, maintaining stable time loops in order to cause a massive amount of future erbium to exist in the present. Of course, this is necessarily a temporary scenario; the time loops eventually end, and the material returns to its origin time, and in the end the quantity of erbium in the market goes back to what it was before. So, flooding the market with future-materials does not permanently decrease the value of the metal.
Maybe most relevant to your question, there are lots of materials which could only reasonably be made useful in a world with time machines. For example: Astatine (or any of those man-made elements which only exist for a few ms at a time). It's got a really short half-life, so making anything useful with it before it disappears is very difficult. However, if you could trap it by constantly sending it to its prior time-state, you could find uses for it. Metals like this would be necessarily rare because of the technology required to stabilize them, and their uses could be any kind of scifi stuff you want. Maybe when we finally have a George-Washington-Carver-of-Astatine appear IRL and find some great uses for it, we'll discover that it makes great laser guns and lightsabers. Who knows!
How Time Machines Change the Raw Materials Economy
The stock market depends on uncertainty about the future. We buy stocks in Company X because we think they're going to succeed, and we want to see the value of our stocks increase. Company X uses your investment to increase their odds of success, and everybody wins. But then, Company Y invents a new disruptive technology and Company X goes out of business. If we could have predicted that, we wouldn't have ever invested in Company X. So, publicly traded companies, investments, and venture capitalism can't exist alongside time machines. In fact, competitive economics break down almost entirely -- we know who will finally make the best item of X category, and so we really have no choice but to give that company a free monopoly over that item... but monopolies are harmful. Thus, after time machines are invented, we can't be capitalists anymore. The only possible economy is one where the price of every item is regulated -- maybe communism or socialism. But if you want to avoid the corruption that historically comes with a few individuals controlling all the means of production, I'm thinking some kind of technocracy where the algorithm performs the role that a far-left government would otherwise perform, regulating prices and basically owning every business.
So, let's say the price of your raw material is determined by the technocratic algorithm. The algorithm measures and decides the needs of each sector of the public, and redistributes raw materials according to whatever goal the algorithm was designed to have. Is it to make the most people comfortable, or to make everyone equal? Does it prioritize defense, devoting most of its materials to military research, or does it prioritize art, distributing its materials to public infrastructure? Either way, the value or a raw material is determined by its priority in the algorithm, and the algorithm might not trade money for it; it might just take the material as its due.