I dunno, you can spend a LOT of money leaving it stock. NOS dash? Rare stock parts that no one has anymore? lol you get the idea.
best thing you can do. Find the most rust free car you can, WITHOUT any electrical problems. Even if the engine is shot, it saves you a TON of money and headaches. I know this personally haha. My 78 has a perfect body, 90-99% of the wiring harness has never been messed with (pulled up the carpet and gutted the interior, and ALL of the body's harness was still taped to the floor, with 30 year old duct tape) The engine has some issues to work out, but you know what? At least I don't have to hunt down a Phantom Short!