I got Frog Togs pants a few years ago and aside from the lining shredding a bit where I shoved my knee high muck boots through, they're awesomely waterproof. You would never think it if you hadn't seen this type of material before. It's almost paper-like in feel, but rip-stop crosshatched. And for $19 you cant go wrong.
I stood with the pants on over the boots in the SURF and the pants kept the waves out of the boots! I was bone dry, totally 100% waterproof, yet not sweaty at all!.
They're zippered at the ankle and come in XXXL.