my recipe: Buy a complete project car , one as solid as possible, One that YOU can do the body work on and have the quality car YOU demand. But it for what it is really worth!!!! If you ever sell, you made your money when you bought, nit when you ell.
Don't get caught up in the "have to have the best, the fastest, the coolest". Unless you can afford to toss those $$$. Network and find a good running engine ./trans worth the $. Rebuild carbs, use OEM intakes, exhaust manifolds. Make a safe dependable driver, first, then as you drive it, repair the rust, drive and work on it as you go.
Do the body one section at a time if you must, spray epoxy primer as a sealer over the finished filler. Sanding primer over that, work on it as you go. Nothing can be more of a drag than to take a car apart , it sits for months, years, decades!!!!!!! Unless you want a model to car to make PERFECT and work on it for years, with nothing fun to drive to keep up your interests.???
Finish the interior last. Have a decent set too sit on, carpet, headliner, door panels, upholstery can come last.
Save $$ he asked? Do not catch a case of "perfectitis"!!!!!! Catch the hotrodder's bug instead.