If you game every week into the forseeable future, then a small-world game might not satisfy you, and you might want to invest in a game that will produce supplements. Once you do this you have several options. You may produce your own supplementary material for the game and run with that. You may search out fan-authored supplementary material on the web. If you want to buy the supplements but don't have a lot of money, you still have a few choices.
Some game stores offer inexpensive memberships that give discounts.
Some on-line booksellers offer discounts as well, or free shipping at least. If you choose your game line wisely and do a little shopping around before buying supplements, you can limit your purchases to the supplements that you really want. If you have a large enough gaming group, you might each buy a few books and share them. You could institute a rule that anyone who wants to play something that requires a supplementary book has to buy that book and let the GM look it over. If the player doesn't have the money, then you stick with the info in the main rulebook or make it up yourselves.