where is the cheapest too take my 2007 pontiac grand prix to have the power window fixed?

There's two major components behind your door panel. The window motor and the regulator. If you click your button and you hear your window try to go down then it would be safe to say your motor is fine for now, and you would change your regulator, if no noise is apparent then it's possibly your motor. That's the major situation. Although I recommend checking fuses before dwelling into that. This is not a difficult task. To save the most money I would do this repair myself. If you are not comfortable with attempting this and possibly changing out one or two main window components then I suggest calling local mechanics in your surrounding area and get a quote, also you could save a few bucks if you purchase the part yourself and bring it to your mechanic. Think outside the box, venture out a little past your comfort driving zone, finding an inexpensive mechanic is not an easy task. Look a little outside your general area and find a mechanic with a price that meets your budget. Good luck.