Fair price for a certified pre-owned 2006/7 BMW 3-Series?

The only thing "certified" is that it is a used car. Don't buy into the whole certified used car crap, it's just a way to get you to pay more money for a car. You should be spending around $28k - 30k for a xi. If you don't need the all wheel drive, you can get a 325i for chaper (around $25k).