It was originally a black kettle from the mid 70's. Those wheels were on 22" grills from 73-75. Not sure if there is any timing difference on the 18s.
What's it worth... as Kettlebb said, it's subjective. I'd say somewhere in the $20 range in the Baltimore market.
That being said, it's a cool grill and a great cooker. Tell your friend to fire it up and have some fun!