I found this to be an ok site, but it would be much cheaper to go get one from a donor car because you also have to get multiple other parts.
Turbo City - Rock-It Parts
plus, just slapping one one there wouldn't do much, considering the car weighs a crap load and you can't go more than about 5 maybe six psi on the tube without destroying your engine. Even if you run a low psi its still possible you blow your engine, the way to avoid that is to get forged pistons which I've found in a price range of (used) $250.00 to about (new) $700.00.
the Cheapest route is to find a 1987-88 Thunderbird Turbo coupe (I've heard of people fonding a decent running one from anywhere between $500.00 to about $1500.00) and just take the engine and
tranny from that and dump it in to your
stang.(thats what I'm trying to do at the moment, need to get the money to do it first.) Plus you have a bunch of extra stuff after words to take room in your back yard to take up space or to sell XD (even use if you have the correct application.)