If you're Bill Gates, that's probably a reasonable price. For the average Joe, that seems way too expensive. I wouldn't even consider it unless it was in A1-mint showroom condition...even then, probably it's too expensive.
Have you talked to the guy about his price being out of line? Tell him what you said about your 215 cab w/cover. Some people just have unreasonable expectations about what their stuff is worth. Don't kid yourself about the original price of Sunn equipment, though -- some of it was pretty darned expensive. A 2000S rig (head and cab) in 1968 listed at $1295 with covers for additional $42. That's 1968 dollars, a fair amount of money back then!!
If you can't get that guy to budge, then tell him it's his loss and wait to find another cab. They're out there...