price question

A friend has an excellent interstate tank. It has no dents or rust and has been sitting in his garage for umpty years. Painted flat white. The filler cap is the Monza style not the usual Norton style. He doesn't know why it was changed but it is so well done it looks like a factory job. He is interested in selling it to help fund a Bonneville project for next year. What could he expect to get for it, tops?

"tops" is too hard to guess, but decent steel I'state tanks fetch upwards of $500 pretty easily.

I sold one with faded paint, and some dings & scratches for $1,000 some years ago, another with better paint and fewer scratches for around $800 just last year.