Last year I went through this guy: Gary Jorgensen. He's an "automotive consultant," whom my mechanic recommended.

He came to my house, we had a chat about what I was looking for. He did all the searching, brought a couple of cars to my house to test drive, handled the negotiations (he's got relationships with several dealerships in the area), paperwork, registration, etc. then brought the car I settled on to my house and took away the old one.

Fantastic experience. Paid him a thousand bucks, but what I paid for the car was ~$6k less than what it was listed for at the dealership, so I thought it was well worth it.