Chips.....

I myself use Superchips' chip.We have a member in our club who works for them, and swears by them.He has a lot of expirience out there with mustang tuning.We took my stang out for a run with his lap top plugged in,got the info he needed,burned the chip,and played with a few different tunes,and voila,my stangs rocks at the seat of your pants.
Any horsepower gains,don't know !Don't really care.Wasn't getting a chip for dyno numbers,just wanted to get my stang to get customed tuned to run stronger!!
Car runs better,pulles better,and the throttle response is nice !
He tuned in more fuel and timing,fixed my speedo to my gears,and i had him have my fan come on a bit earlier!!

As for pricy,...try living in Canada for prices on high performance parts !