Dude, this doesn't go in the Tech section. Mustang Chit-Chat would be a much better choice.
If you go with Jon Lund, an email tune will run you $200. I highly recommend him. I recently checked him out thoroughly at the recommendation of S197 GT, Nick, and discovered the man is a phenom when it comes to tuning Mustangs. If you go to a local shop, make DAMNED SURE they know what they're doing when it comes to the 5.0L Coyote engine. Not many local shops have the experience needed to tune this engine. Stick with a big name establishment that can actually stand behind their work if they fuck your engine up.
But a dyno tune will usually take two to three hours and run you around $300-$500.