Depends on a few things. Mostly the going rate at the shop of your choice and what year car you're tuning, along with whatever equipment you need (chip, flip-chip with multiple tunes for a modular motor), X-cal, etc.). Plus however many pulls on the dyno you need for them to straighten things out, although some places just figure that all into hourly rates. I know the top shops here charge $150-200/hour for custom tuning and dyno time for anyone walking in off the street.
It all varies wherever you go and by what you need done. If you haven't got enough stuff done to the car I wouldn't even worry about it. What's done on it?