I bought a kit on flea-bay for about $600. It included everything from the peddle to the wheel including new wheel bearings. This was a front disc conversion only. Adding the rears adds about $300 and doesn't add much more performance. Make sure you find one with the brake lines in it. You don't want to mess with that if you can get stainless lines pre-bent and flared.
It took about 2 weekends because it was my first project on the car. Actually the first time I've worked on any car older than 1988.
Some valuable lessons learned: Do NOT get drop spindles. Just don't. If you want to lower the car at the same time you do this cut a coil off the spring. Drop spindles change the geometry of too many things and really screws up the handling. Not to mention that when you put on disc brakes it'll push out the front wheels roughly 1/4". A 2" drop with that extra 1/4" out means you might rub. Or, as in my case, you'll rub so badly that you can't drive it.
So, like I said, NO DROP SPINDLES.
other thoughts: get a rear brake line kit at the same time you buy the front brake conversion kit. Trust me. You can do what I did and go to autozone and buy new lines there then bend them, etc, etc. You can do that but it'll take you several extra hours and only save you about $50 in the end. Not worth it to me.
Adjusting the brakes can be a bit of a PITA. Take your time.
Oh and get a set of gear wrenches for the booster. You'll thank me later. Surprisingly enough the set I bought at Harbor Freight are really, really good. You can sometimes get them on sale for about $20 a set or less. Worth every penny. Without it I don't know how I would have gotten the bottom two nuts onto the studs holding the booster to the firewall.
