If it is clean, working and not hacked up,and you are wanting a SSB radio, I would give 40 for it, they are a good SSB radio for a standard 40 Ch radio.
I would always try to talk them down
It would be best if you can test it before you hand over the cash....if no mic that is going to be hard and that is going to reduce the value.
Here is one that has been converted to Ten meters on YouTube
CB TO 10 METER - RYSTL CB4082 - YouTube
I had the JC Penny 6247 and I am almost sure it is the same board, had a lot of fun with that radio.
Make sure it is a 40 channel radio. There was an Australian model that only had 18 channels ( CB 4082 A-18)
Lou Franklin s Golden screwdriver Guide has the tune -up info listed.
VR-4 (the big VR on the left side of the chassis) controls the carrier.
VR 12 on the board controls the AM Modulation level
VR 2 on the board controls the SSB ALC
it also has a Adjustment for SSB mike gain on the board VR 11
If it is in good shape and you do get it, post some pictures of the radio.
73
Jeff