I actually had a discussion with my doctor on this very subject. He was complaining that he could not actually advertise prices as it is apparently considered price fixing if doctors do that (or so he says). He also told me he would be stupid not to bill the highest possible price he could for things because he doesn't know exactly what the insurance companies will accept and he could be leaving money on the table otherwise. So don't try to distinguish between specialists and GP's, they all do it.