There are only a few exhaust mods that might effect the tune. Bill could talk to you about those. In general, adding an exhaust mod does not require retuning at all, and, according to several discussions I've read, most exhaust mods have very little effect on performance too. About all many of them seem to do is change the sound.
I'd say get the programmer now. It WILL change performance (for the better) and will probably save you a few pennies in fuel costs - although the payback time is pretty long. Still, if you're committed to shelling out the bucks for one or the other of these mods, the programmer's the one I'd go for.
- Jack