I'll give you $50 for it, no questions asked
Seriously, the answer would probably depend on the state of the primary mirror. A new 16" Dob is probably pushing $1500-2000 brand new, but few are solid tube these days (must be a beast to lift!), so maybe towards $1500 (new) as solid tubes seem cheaper than similar truss tube models at Bintel.
But with no cover on the top, the mirror may not be in such great condition any more (??), so quite apart from it being second-hand, and lacking the mount, that could knock something off the value. I also see that a 16" primary mirror from Bintel retails for $1600 - the mirror's your main asset so that may help determine the "as new" value. Perhaps ATM types might be interested in the optics?