I agree with jlm, probably a Japanese 15 clone, which are good machines overall...but want to say don't expect to sell it for a lot. "Most" people don't appreciate the older machines, and there are actually millions of them out there. Not rare, not actually "collectible" except by a few weirdos like us!
Price depends so much on condition, what attachments come with, etc. Do you have a picture or two?