A buddy of mine sold a 1929 Ford 2dr sedan last year for $5,500. It was really quite solid, though it was also a non-restored original, so it needed some work.
Prices are always based on supply vs demand. They built a lot of Model A's, and there are still a lot of 'em out there. And I think the popularity of them among the younger set is dropping off. So I don't imagine the prices going much higher than they are already...they might even go down some. Take for instance, the cars from the early '20s and teens. I've always been surprised that generally speaking, (depending on the make and model) you can buy one for quite a reasonable price. I don't think many younger folks are really interested in them. And the Model A's are closer in design to the earlier cars than they are to the later models.