PixMasters is the other most known site with inexpensive content. I would guess theirs is a lot less exposed than ZipContent's. You can read the GFY thread with not-very-happy people.
If you want HQ stuff, we have many smaller sets under $20. A lot of our new releases will be things the surfer has never seen. Get a 5th freebie set with every 4 you buy. Or we have discounts for large purchases.
http://www.XPhotography.com/