The high is completely up to you. Don't get emotionally invested in the car. That's an easy way to spend too much. However, in just a few years, what you spent on it will feel like a bargain, almost regardless of how much it was. (Within reason, of course.)
How desperate is the seller? How desperate are you?
Before you shell out any money for the car, run the PHS. (Unless, of course it's in great condition and he only wants $5K for it.) I was once contacted by a buyer AFTER he bought a "Sprint" only to find out that the car was originally a 1-BBl car. He was unable to resolve the issue with the seller. It may have gone to lawyers to settle the matter, which was easily avoided if he'd have done all his homework before buying the car.
For the car you describe - being a convertible - it probably would be reasonable to expect to pay between $15K and $18K if it is truly a Sprint. The 4-speed option is less common than the 3 speed. The trans is probably a Saginaw. Peek under the car and see if it's a steel case transmission or an Aluminum case. If it's too dirty to tell, the magnet you brought along to look for bondo will come in handy. Compare your results against the PHS.
There's NOTHING in the VIN to tell you whether the car was originally equipped with a 4-Bbl. You must run the PHS. ( www.phs-online.com ) They have Fax-Back service if you are in a hurry. One word of caution, though, is that the PHS is not always 100% right. You have to compare it to the billing history to be certain they've done their high-lighting correctly.
