So I'm always on the look out for cheap DIY materials that you can make at home, and found this nice video on how make a pseudo-plastic. Pseudo-plastics are plastics that are almost like a plastic but aren't exactly like one.
Styrofoam is pretty cheap. You can probably find some in your house, in neighbors houses or pick some up at your local recycling center...
Though a simple google shopping search finds me acetone and packaging peanuts... though I'm sure you can find either at home depot or packaging store. Acetone is in nail polish remover, but you can buy a quart Rust-Oleum acetone for $5.
The end result as you can see makes an interesting clay substance. Though, I'd highly recommend using gloves when working with it, acetone burns.