My Caddy cost me $250. Body was ratty but solid with minor damage but no rust. Ran perfectly but trans was bad. First 2 days I owned it, a friend and I spent both days cleaning it up (the trunk contained half a barrel of trash, two old tires, a broken 4-way, and a dead squirrel), swapping in a junkyard TH400, changing the leaking valve cover gaskets (and discovering a neglected engine loaded with crud), flushing the coolant, getting a good battery, doing the brakes, throwing together a temporary exhaust system, and putting on 4 good used tires to replace 4 different brands, two different sizes, and three radials and one bias ply. A few weeks later, I replaced the ratty old carpet and scored a matched set of non-wire wheelcovers. It cleaned up surprisingly well, and I drove it...put over 60K on it, including a drive from New England to Arizona and back. (If you're curious: 9000 miles of 1500 mile changes with 15W-40 Delo to try flushing the glop out.)
A few months after that, I decided to fix the balky power seat motor. That entailed removing the seat. With the seat out, that seemed like a good time to fix the headliner that was held up with packing tape. At that point, my wife noted the paint on the roof was badly lacquer-checked and the landau top was pretty ratty. With the seat out, it would be easy to pull the rest of the interior and paint the car; she suggested the shop that painted her Grand National...and the snowball began rolling. A year and a half later, the entire body had been stripped to bare metal, completely repainted in Tuxedo Black, the landau top deleted, the headliner and front seats redone, the front suspension rebuilt with Impala SS parts, and the rusty decklid replaced. Engine/trans went back in, drove the car another ~10K miles...then the head gasket went.
Hitting swap meets to try and find someone parting out a Caddy with a good engine, I found someone selling a stroker that had been in a Chevelle that got wrecked. I bought it...starting the second snowball rolling.