You can find the odd Powerdyne 6lb kit on the Corral for $700-1000 USD sometimes, for a good complete kit. Factor in a fuel pump, injectors, adjustable regulator and a tune and you're golden. So for under $2k your car will have a reliable 300hp and be lots of fun to drive.
Personally, on an 86 GT there are a few other mods I would do before a blower. Most would suggest doing a Mass Air conversion, but with a tune the Speed Density system can work very well with a blower. I would definitely upgrade to the 87+ E7TE heads and intake, but if you're willing to spend a bit more you can always find good used Explorer GT40P heads and intake which flow substantially more than the stock 87 pieces. Upgraded exhaust should also be done, and if you're planning on a blower then 3.73 gears would probably be best.
SS