it's not bad at all, and can be cheap, if you're handy, expensive like he said, if you're not.
You should be able to get an oem upper/lower intake from an efi mustang for free or close to it from just about anybody. Put up a wanted ad here and on the corral.
go to the junk yards and score the efi lines, front to back. Bring a cordless drill to drill out a couple of rivets, and a socket set. Simple. You'll need a sender from an 86efi car, specifically, NOT an 87+, or your gauge onyour foureyed cluster will read backwards. You'll also need an efi tank/pump, again, simple. the lines will bolt right onto your frame, (drill for bolts where necessary) the tank will go right in, and the upper/lower intake will bolt right on. the difficult part is the wiring. if you're not running a cam, then speed density will suit you just fine, and are a dime a dozen in the yards. Grab the computer, and computer harness.
two ways to hook up. the easy way is to call windsor-fox.com. for a few hundred, you ship your harness to him (go mass air if you go this route so you don't have to change in the future) he'll modify your harness to make it plug and play with your oem 84 harness, and tell you how to connect it. the other route is to splice it in on your own, which is simple from what I hear, but you'll have to find the guys on foureyed pride who can tell you this. the final way is to grab an entire 86gt wiring harness, front to back, literally and swap all wiring into your car.
sounds like a lot of work, but it's a mod that will well pay off.