Just remember... what you pay for is what you get! I think prepping it yourself is the best idea, and just having them spray it. To prep it, you'd have to remove all the moldings and stuff to get as much paintable area exposed as possible, then wet sand it all down, smooth out any bodywork, then prime. A coat of primer will reveal any imperfections in the body and allow you to fix and make repairs. Good luck!
Jeff
Jeff