I've seen Ithaca's normally run in the $400-$500 range, depending on the gauge, barrel length, finish, etc. But from what I've heard, the older model would be the one to buy. I've heard that when the company went through hard times in the mid-late '70s, quality went down the toilet and the company was pretty much run into the ground. Now that the company has been relocated in the mid-west, the new owners are bringing back the quality standards Ithacas were known for.
Avoid the '80s model, and go for the early '70s model.