Almost 20 years ago now restored my old Pontiac. Unfortunately it needs it again, after almost 10 years of daily driving and being parked outside. It's been garaged since we bought the house in '93 but I've had zero time to work on the body. It's got about 270,000 miles on it.
I did my restoration in 1983 after somebody hit me and wiped out the right front corner. At that time, I replaced the hood, right front fender, grill pieces, and the front bumper was straightened and rechromed. At that point I could still get some NOS (new old stock) parts from certain Pontiac dealer/distributors. No chance of that nowadays, but thanks to the fact that this car shares much of its sheetmetal with the GTO, the reproduction industry has come lightyears since I did it.
I sanded the whole car down and cut the rust out. Fender skins were unheard of at the time, so the rust was all repaired with Bondo. The way to do it now is to buy steel parts such as partial fenders (just the rocker panel or wheel arch depending on where they commonly rust) from a restoration catalog. Then the cancer is cut out to the correct margin and the new piece is welded in place. If it is done properly and ground smooth it is unnoticeable.
So I sanded, filled, sanded, filled, and primed. I decided to change the color from the original pale champagne color to the correct Pontiac Rally Red for that year, which meant painting inside the trunk, all the door jambs, inner front under the hood, etc. We set up a spray booth in the garage and a friend of my father's put the finish coats on (about 4 coats of red laquer).
In retrospect, I should have stripped the car bare. That's what needs to happen next time I get it painted. That's why it hasn't been painted in 20 years.
At the time, I also bought new carpet and a new top from J. C. Whitney. I pulled the interior out and cleaned the heck out of everything, and installed the new carpet. My then-girlfriend-now-wife sewed up a few rips in the upholstery. I sanded and prepped the top frame while the canvas was off, and rebuilt the hydraulic cylinders to the best of my ability. I shot the top frame with a fresh coat of gloss black, and repainted the inside of the trunk with splatter paint. I also bought new trunk liner material and cut it to fit.
A few years after that I bought the Rallye wheels from a junkyard and refinished them because the hubcaps wouldn't stay on it and they were getting hard to find.
How much did all this cost? I couldn't begin to tell you. But it's not cheap. Check out
http://www.yearone.com/ for probably the biggest and best supplier of repro and NOS parts around.
Eric, a couple of things you need to decide for yourself - do you have reasonable mechanical skills? Do you have time/money to invest? Do you have tools and facilities? My father helped tremendously with this project and now that he's dead I would hesitate to tackle it so throughly myself (unless I was made of free time). I wouldn't even consider it if I didn't have an enclosed garage that I could use all of for a long time. To do it right you need to be able to rip the car's guts out and protect it from everything for an extended time. Think hermit crab between shell changes.
To do this right you need three things - time, money, and skill/facilities. Lacking any one of those is going to take a lot of the other two to make up the difference.
All that being said, yes, someday I'll refurbish this car again. I won't
begin to recover the investment it will take, but I have a lot of sentimental attachment to this one.
If you decide to go for it, above all
be patient. Decide what kind of car you like and will want when the project is over. Then spend a lot of time and research checking out the cars you're considering - there are online clubs for just about every car imagineable, and they can tell you what to look for and what to avoid. Be very fussy about the particular example you buy. A few thousand dollars extra for a little nicer condition vehicle can pay for itself many many times by the time the project is done.
Hope this helps! Feel free to ask any specific questions you've got; I may be able to help or at least point you in the right direction.