There is a Dynavector for sale here at Audiogon for $275.00. I don't know how that model stacks up against yours, but it is a starting point.
As old as yours is you may have to play it to be certain you have a good working piece. Only other option is sell to a person who you can trust and give them a week (or other time period) to try the cartridge out to be sure performance is good. Selling used cartridges is difficult at best, I am struggling for ideas that would be fair to all concerned.