How much do show quality pitbulls normally go for?

There are two major lines of pitbulls, and the newer breed do have very bulky shoulders and huge heads. People do pay prices like that and higher for show quality dogs, but as far as pits are concerned there is another reason people buy dogs for that price, especially ones from bloodlines with a larger musculature. It sounds like your neighbors may be breeding fighting dogs. I don't want to jump to conclusions but if there's any chance you should contact the authorities.