You know all those election signs and real estate signs you see stuck all over the place? They're all made of some stuff called coroplast, or corrugated plastic. Coroplast is to corrugated plastic as Kleenex is to tissue. That is, it's trademarked, but because of its success it has become a genericized trademark. Ok, enough with the history lesson.
If you're a little short on funds, you can hack some pretty nice fenders out of coroplast. The stuff is easy to work with, weather resistant, and in abundant supply. Kent Peterson has several entries on using the stuff for crafting your own fenders (and other stuff) from coroplast.
This is the height of bike hacking and I love it. Kent's also got a killer tutorial on building panniers from coroplast.
Visit Kent's blog and type "coroplast" into the search bar . . . and then just wait a few more months for election season and have at it.