where is a good place to ranch cattle

Well. . . if you are already in Montana . . . there are lots of places there!
If you are interested in this, you should join the FFA at school, where you will learn a lot.
There are many things to think about when buying (or leasing) land for cattle ranching, other than just the price. For example, the availability of water and shelter, proximity to a large animal veterinarian, distance to market, predators, fencing, weather, etc. There is also what is known as the "carrying capacity" of the land. That is, how many acres do you need for each animal? I've heard it takes 5 acres per head in west Texas, due to the aridness of the land, but I don't know if that is correct. Where do you want to live? Do you like the snow? In the hotter/drier areas, you might have to buy hay for your cattle. In places with adequate rainfall, you may not need to do that. Lots of variables! It's good that you are researching now!