Like Jed, I use to do it myself, but for the exterior, I can't anymore. It takes too long. My car is black, and it takes about 4 hours+ for me to wash/wax/polish my car, and that's with a one step wax process, not 3. 
So last summer, I got the exterior detailed for the first time. I decided to go with the "You get what you pay for" approach. What a mistake. I paid an absolute fortune for it by going to this place which apparently does exotic cars. When I got the car back, it did look good. No streaks, no wax marks, etc.... But then when I got home, I noticed that when the buffed down the wax, the brush they used hit the rubber around the windows and scratched it... Now scratched rubber really shows...
Also, underneath the spoiler, they wore the paint down to the plastic. So it doesn't really show unless my hood is open, but still. So overall, I wasn't impressed at all. So in my opinion, price has nothing to do with it. Go with reputation. Don't blindly pick a shop, ask around for recommendations.
As for my interior, I always do that myself. For one thing, I keep the inside of my car clean (it still looks new) and to armor all my dash and treat my leather only takes an hour or so and I only need to do it once or twice a year.
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