I've been looking at things online and you can get some sweet collections of things for pretty reasonable prices (considering the quantity). I found this tube of 97 plastic figurines at Target for $5.00. I don't have much use for the green army men, but the monsters are pretty neat.
Below you'll find pics of some of the favorites I've found on Amazon (hyperlinked to take you to the product page).
No they aren't painted and yes they're the little plastic toys like you played with as a child, but each of these packs is 17 bucks or less and if you don't mind the scale, they're a quick way to build a collection.