If there is an Industrial PPE Company (Personal Protective Equipment) in you area, and see if they will sell you one or two Tyvek coveralls. They come with or without hoods, with or without elastic cuffs, and are individually only $7-10.
They also make Tyvek Lab Coats, about the same price.
Some Sears locations carry coveralls, but I don't think they carry white. Some NAPA locations carry used coveralls, but I don't know how widespread that is (I have only seen it at one location). You can also try ACE hardware, but that will vary store to store.