did you check ebay cause i have seen them on there for no more than 2000There are cheaper kits out there.
Go the the info section of this site Mustang Turbo Kits
I have seen this kit on a local's car and it is very nice. And it is only $2900 for the base kit which is a single 70mm turbo and such...Of course for more money he can get you whatever you want.
Also, what block are you running? If you are going to do it RIGHT, buy a dart or world products block.