So you already have a place who'll tune it, you just want it chipped? Have you ever soldered before? The parts to chip an ECU are about $30. I've done many myself and it's a lot simpler than you may think. Tuning is pretty easy. There's plenty of maps available for damn near any motor set up you could ever have and it's as simple as drag and drop, click save. I've never sent out an ECU before but as mentioned above, those seem to be the names everyone talks about. But if you have a legit tuner who can tune your car on the spot, then obviously that's the best way to go.
Good luck!
EDIT: Also, you don't NEED a P28. I like to chip P06's because they're cheaper and can be modded to do the exact same thing as a P28/30/72/ect ... But if you already have an ECU, then never mind. LOL