"would you pay $750 for an A that needs carb, alternator and potentially a radiator?"
Probably not. You have no way to start it and determine if the engine, clutch and transmission are good. If you can't repair the radiator and have to replace it, a new one is $366 to $448 on this site. You can't even fill the cooling system to see if there are leaks or cracks in the block. A carburetor on this site is $203 to $353. You didn't say what condition the tires are in, but that can be a $500+ bill if they need replaced. You are starting out looking at several hundred dollars in parts needed before you can even try to see whether the engine is any good. Did you check to see if it is free, not stuck?
To me, and this is just my opinion and worth only what it cost you; $700 is a very generous offer. I'd be at more like $400-$500, and then only if the engine isn't stuck, it's still taking a chance.
Others may see it differently.