It depends if you want the paint job to look great, to look ok, or just to look. It also depends how long you want it to last - long enough for you to sell it and change your phone number, or really for the life of the vehicle.
Doign some of the prep yourself will help but you mnigth want to make sure you are doing that right in the first place! When I was getting my truck painted, I tried to save some money by having a co-worker do some of the prep, he did a pretty bad job of it and the body shop had to redo it plus some anyways.
If you want like a show-quality paint job that will last years and years, and are changing colors, expect to spend several thousand dollars... if youw ant to repaint over your existing color with the same color and just want it to last a few years you can have maaco do it and save quite a bit of money.
Just FYI, when I had my truck repainted, it ended up costing about $7000. Part of that was fixing hail damage, a few accident dents and dings, and a full color change with flames, and that was after he gave me a decent discount. The paint itself is cheap, the prep work is what'll get you. My truck was in the shop for nearly 2 months (not being worked on full time though), and only took a day to spray, do the flames, and clearcoat).