Do an internet search. The prices vary- there was a very nice original which needed to be restored but looked clean asking around 3700+ a year ago. It sold, not sure at what price. Everything is more expensive than a year ago.
I don’t know the market but since few people have dedicated mono set ups your customer may be somebody who has one and is looking to own a stereo pair. It is an interesting amp, certainly one of note. Condition is going to factor into price, as will provenance (if it has any that you know of). The compressors are crazy expensive now- rare as hen’s teeth.
