There are TONS of inexpensive carded figures for sale all the time. And if you only want to consider figures under $100 than that still leaves you with, IME, a good majority of figures that are bought and sold. Take a look at my collection (website in sig). I won't say exactly what I paid but I will say that the AVERAGE price I paid for each of the figures is between 50 and 100. And I've been pretty picky over the years. And don't get me wrong, it's been ALOT of work, patience, research, and occasionally risk taking.
As long as your standards aren't ridiculously high it sounds like you could build a fantastic collection.