You are going to pay at least $100/month to own a car, whether it is old or new. It's a "pay me now or pay me later" proposition. Buying new, you pay for all-new parts all at once. Buying used, you replace wearing parts one at a time before they threaten to break down. Plan well and you'll do the work when you want to (not when the car fails).
Buy a vehicle that can be repaired easily and cheaply. Ford Mustangs, Camaros, VW. Bugs, 1/4-ton pickups, and other popular vehicles, every part but the frame and body shell are available at a reasonable price. Look in the catalogs or call local body shops.
Whether you or a paid pro does the work, you'll have to know what your car needs and what your options are. Read car-restoration books from the library. Subscribe to the old-and performance-car magazines and catalogs. You'll surely need same help, and every country town has genuine and self-styled experts on restoring old cars. Ask anyone you see driving an older vehicle who they recommend for mechanical and body work—and more important, whom and where to avoid.
Parts may take some searching. You can save time and money if you buy a parts car to cannibalize or scout around for a car like yours that someone got tired of working on and that's being "parted out." Use (well-) rebuilt alternators, starters, and, other wearing parts and junkyard body parts when you can.
With other than for a "numbers-matching" show car, substitute modern parts if possible. For example, GM refused for decades to spend more than $2.00 for an electric clock—even for Cadillacs—so clocks never lasted long. Using Velcro, I stick a $1.00 digital timepiece over busted clocks rather than buy a "NOS" GM Clock movement listed in the catalog. NOS means New Old Stock: original unused repair parts that have been stored for decades. You pay for the storage—and an NOS clock won't work for long if it works at all.
The more you replace of a failed or worn system the cheaper it will be in the long run. A rebuilt Chevy 350 engine block and heads costs $754-1,500 stock, $2,500 and up for an over-bored block, bigger pistons, a hotter cam, and more horsepower. Not cheap, but less money than diagnosing and repairing an endless succession of problems. While the engine is out of the car, replace clutch parts ($100 + labor), and as much else as you can afford. Have your carb rebuilt by a pro ($10 p.l.) or buy a rebuilt ($120) stock carb or hi- performance replacement carb ($2500) and intake manifold ($100). Bolt on a new water pump ($40), a fuel pump ($25), timing gears and chain ($30), and other parts that aren't part of the rebuild.
Don't fix just one worn or leaky brake—do 'em all while the tools are out and the car is off the ground. And, rebuild the whole thing: new hoses and wheel cylinders, backing plates, rebuilt calipers, and new drums and rotors.
It is usually cheaper to replace whole body panels than cut out rust, weld in patches, and smooth with lead. (Don't use fiberglass/plastic—Bondo—to patch a great vehicle.) But, shop hard. A used door that may rust out in a year costs $250 at a junkyard. A NOS steel door shell can cost more than that, while a new Taiwan-made door shell costs $95 and new door and window gaskets about $20. Prime and paint the metal inside and out, and move window and latch mechanism yourself. Be sure the drain holes at bottom are open, and the door will last for decades.