Im not too clued up about cycling specific gear, but I have some ex royal navy goretex overtrousers from an army surplus shop for a tenner.
Nice waterproof, breathable and, in the case of the ones i bought, had nice velcro around the ankles, meaning i could tuck the flappy bottoms in nice and tight to avoid it catching in the chain!
Not perfect by anyones margin but for the price, if i really dont want to get wet then they do the trick (commuting to work/shops, touring etc)!
I have to be honest though, if im going out for only an hour or two for a bit of exercise, i just usually get wet, it doesnt matter to me, i can dry off when i get home.