I used bibs with ankle gaskets and a dry top for several years in the winter. I took many swims and would only get slightly wet in certain areas around my ankle or chest.
I saw the same bibs for sale down in Portland this weekend at Next Adventure.... I think they were only around $100-$120. They have a great new paddle store down there and might be available online.
About the waders... I don't have any personal experience with them... but if something is as good at keeping water out, it would also be good at keeping water in.
This sport requires specific clothing to keep you safe. The bibs I am referring to had a double tunnel you could roll up into the dry top... The waders I'm guessing wouldn't have anything like that.
My $.02
Kirk