Appraisal is about $5, that is what you paid...seriously - I would check the auction sites for those units, marked sold.
To the right buyer you may get a hundred, but they don't seem to demand a "snap-on" price.
We used one in the mid 70's at a Gulf station I worked at, and in the right hands they were awesome. Of course this is in the day, when we actually changed individual plug wires, when one was bad. And as a pump jockey, we checked oil and did the windows.
Best of luck.