Better to buy a decent car at a decent price. In today's market $30k will buy a lot of car if you know what to look for. This is coming from a guy that has never bought a "finished" classic car. Yes, if you do all your own work you can break even or maybe even come out ahead. But its not easy, and it will require a ton of time and a well outfitted garage. If you don't have the tools already, you'll spend thousands just in tools to get your basket case running. What do you want out of the car? If you want to drive it and have fun, spend most of your budget on the car. If you want to restore something, buy a solid project and go from there.
I bought my Challenger for 11k. Trust me when I say it looks much better in the picture than it actually is. So far, I've replaced and upgraded ALL the suspension, welded a patch into and reinforced the rusty front framerail, changed the carb and intake, and purchased enough parts to do most of a 4 speed conversion. I've rebuilt a 340 for it, and made a few cosmetic upgrades. I still need to replace the driver's floor, part of the rear frame rail, and about half the interior. With the engine and suspension work alone I have another $10k in the car in the last year, and the engine isn't even in the car. And that still doesn't address the bondo thats rusting out my quarter/roof seam (among other places) that's going to require an entire body/paint job in the very near future. When I finish it will be what I want, and I'll probably have close to $20k in the car. It will likely only be worth around $30k if I'm lucky, but I didn't set out to make a profit. At this point, I wish I had spent more money on a rust free car that I wouldn't have to redo all the bodywork on. A basket case car is a HUGE undertaking, even for skilled mechanics. My Challenger has been my daily driver for the last year, but I suspect its been more work to keep it on the road than most folks could handle on their own in their garage. I grew up restoring cars, and still have access to a full shop in addition to a garage that's getting pretty respectable (MIG welder, high capacity air compressor, engine hoist, stand, several large benches, drill press, 12 ton press, etc...). Half of which I had to get to do something specific on the car. Don't get me wrong, I had a pretty good idea what I was getting into when I bought it, and although it may not always sound like it I love to work on my cars. Which is why I bought something that I knew I would eventually spend $20k fixing.
My advice? If you've got $30k to spend, look for a $25k car. Unless you find your "dream car" ie, a car set up exactly as you want it, you can use the other $5k to get started on making it "your" car. You should be able to get a pretty nice, solid car and still have some money to put some goodies on it to get it the way you want it. That way you enjoy your car right away, not worry about learning how to restore old mopars from day 1, and take on the projects and modifications as they come.