They're not as cheap as you think, either, at least for people who are willing to negotiate their image prices.

I haven't found that at all, I do a lot of illustration type stuff as well as design element stuff  (I hope that makes sense) and have found them really bad at pricing these properly or repricing them when you contact them. They don't seem to realize that a complex/ high quality character design often takes longer to create and has less universal appeal than generic design elements so needs to be priced appropriately. I guess maybe it is just the wrong site for this kind of work and I should have just uploaded design elements there.
In any case, I gave up on them a long time ago and they just have my old stuff now.