With a simple bolt on like that you don't need a tune. A REAL tune will cost you 300-400 dollars or more. You could advance your timing a few degrees and get a couple more HP. Until you upgrade heads, cam, or injectors, there is no real reason for a tune. The stock computer changes the timing as you drive (which is different from the base timing that I just mentioned) to be efficient as possible.
1998 GT - CAI, trickflow intake, 3.73 gears, O/R x-pipe, flowmasters, short throw shifter, 24lb injectors. 155k miles
1995 GT vert - 1 of 36 5.0 Appx. 400,000~ factory motor miles (totaled, in garage)