That's a difficult question too Dan. Generally, but not always
, the more you pay the better the car should be. In most cases, you can't restore or build a car for the price of a first rate one.
As with most old cars, the primary issue with these cars is the body condition. They rust just about everywhere. The most critical area is the bottom of the A pillar and adjacent inner sills. Rusty outer sills is a give away, but they may have been repaired without fixing the inners. Rust in the front subframe in the cross member under the radiator is normal and fairly easy to fix, rust in the rear subfame legs where it joins the body is also common. Rusty floors are fairly standard and if bad can result in rusty underfloor braces. Then there's the front guard peaks near the headlights, round the front and rear screens, doglegs, bottom of the rear quarters, boot floor and of course doors themselves
You need to get under the car near the A pillar and carefully examine the lower guard, inner sill and A pillar, subfame and under floor cross brace. The good news is that if this is good, chances are the car will be good elsewhere.
In my experience - others may disagree - for a pretty decent car without a lot of rust $4,000 - $6,000 plus seems to be a starting point. From there it depends on what needs to be done, how original it is etc.,. Restorers will pay more for a decent original interior and original engine, modifiers don't care. Generally though, buy the best car you can afford, it will always cost less in the end.
Hope this helps
John