Dealer prices are usually outrageously expensive compared to a decent mechanic, but on the other hand I've experiences that tell me that some mechanics are sharks so it's important to establish a good relationship with a mechanic or learn to do it yourself.
I had this other experience where a Ford dealer tried to sell me a car and even after I told them my situation (no credit history) they insisted that they could "help" me, so when the salesman had to go get the manager; the manager sat down in the salesman's desk and after looking over some papers he started subtly laughing.
Another dealer had a car I could afford but wouldn't do test drives on Saturday (basically the only day I have to myself), so ultimately I ended up finding a nice little Volkswagen on Craigslist from a private seller.
So dealers? I could do without them.