According to the capcom price guide online (which is sometimes skewed) it says it is a 100-150$ board. Of course, I don't see this one come up often, so it really depends on how fast he wants to move it as far as price.
for the full cab it's a great price. Almost any working board is worth maybe $50. This board is at least worth $100 for a A+B set.
The rest of the cab depends on how good the monitor and what cab it's made from. If you are talking a big blue or a nice dynamo... this could easily get to the $300-500 range.
Don't forget price is always dependant on...
You mention this being a "dedicated cabinet", but to my knowledge this game was only sold as a kit, so there was never a dedicated cabinet for it. That being said, any cabinet working for 100$ is usually a good deal, just for the working monitor alone.
However, in this games case, if the game still works (the PCB), you are still getting a good price at 100$ for the game, even if it was just the B board alone you are right on the low side for it.