No significant dents, pads have good life left in 'em ? Not filthy inside ? $1000-1100ish.
If buying, that would be a fair offer. If you like to put a sellers nuts in a vise, offer $850 see what they say. Your argument would be "the later and arguably better 8XX series horns go for around $1300 in playing shape these days"
If selling, and you are in no rush to sell, and you are good at marketing verbiage, price it at $1300 and accept offers.