There are 4 things I would gladly pay a pro to do for me: rebuild an automatic, machining on an engine block, welding on items with which my life is at stake, and setting up gears in an axle.
The best advise I can give is shop around as much as you can for prices, experience and warranties. If the gears are set up wrong it can be disastrous. Make sure you use someone that will stand by their work.
Oh, and if you're going to regear, don't skimp out on the ratio. Deeper is better. :D