Hi! Actually, I own one of these myself! 🙂 I purchased one for my son back around 1993 so it’s not quite as old as you think but pretty close. I see you say that yours is 12″, the one I own is anywhere between 25 & 30″ depending upon where it is measured from.
Now for the sad news-I don’t believe these great advertising pieces have much value yet….I have seen these have a tough time selling at both live and online auctions so I would have to assume the value is less than $10. :S