About $2000 if you have it done. Figure a standard MK VI overhaul at $1300 plus some straightening/dent work and a couple of keys.
A good $2000. Maybe more. But to me, this poses a different quandry: since the thing is so absolutely beat, why not go for a custom? Full working order, as many original parts as are left, silver plated, custom engraving. It's already a one-of-a-kind, and as it is, as far as value as a musical instrument, zero. It's nothing but potential. To me it's most attractive to someone who'd want to keep it. I would. (Like I need more horns.)What do you think the price tag is to fix that one up?