A53 1969 Barracuda Formula S Convertible!
Someone looking for 69 340 motor (if it still has it and it's not cracked) would likely pay $2500 for it as a parts car and probably get the motor for free by parting the car out so I can't see it going for much less than that in the open market.
If you're the dealing with the owner exclusively,start around $1500 and see what happens.
Hopefully someone will fall in love with it and have it restored,it would be a really cool and rare ride if it were restored to stock.