I don't get alot of rain but I keep a pair of rain pants that were half of rain set made by Columbia I'm sure i didn't pay more than 50 dollars for in my rack bag, they work well after I added some suspenders to the mix, I'm sure you can find something comparable at any Wally world,Target,or sporting good store.
REI has a decent pair of Novara cycling rain pants for $45. Better brands like showers pass are definitely better (there's no venting in the knees, etc). But they work well enough for me in Oregon and I only really use them when it's a cold rain, so I don't mind the lack of venting.
J&G has very nice rain pants for a reasonable price (http://www.bicycleclothing.com/). As a bonus their stuff is made in America. I like supporting "local" companies if at all possible. My other favorite place to get cycling related clothing is Lou from http://www.foxwear.net . Lou nis great to work with and where else can you get custom made cloths at the same or lower cost than at a local store.