Here's a way I've stretched my miniature dollars while still getting some cool looking figures. In most toy sections they have bags of critters. These tend to be rather cheap, even cheaper if you can find a good set in the Dollar Stores. They have a variety of different animal sets.
Here is a picture of one of the packages which cost me about $4. This one was of creepy crawlers and has 16 pieces. It has a wide assortment of critters in it, which could be used as large spiders, stirges, giant beetles, giant scorpions, ankhegs, giant centipedes, giant worms and other types of insects. For scale, I have included another picture on a D&D battlemap with a miniature of a minotaur for size comparison (you can click the picture for a bigger and better view).