Where can I find a safe and affordable waterproof mattress pad?

Here's a mattress pad with no polyester--only polyethylene and natural fibers. I don't know if it's in your price range, but they do exist. 

If you can't afford this, you can get polyethylene sheeting (like a "poly" tarp sold at outdoor stores for camping) and put it on the bed to protect the mattress. 

Polylaminate is a sheet of polyethylene film laminated between two sheets of aluminium foil.

Debra :-)

This answer was provided by our friend, Debra Lynn Dadd. Hailed as "The Queen of Green" by the New York Times, Debra Lynn Dadd has been a pioneering consumer advocate since 1982, specializing in products and lifestyle choices that are safer for human health and the environment. She is the author of Home Safe Home.