what so you think it is worth
$4000...tops...$1500 bottom....with clear title/paperwork.
Approach it from the stand point that if it doesnt run....it needs:
Battery
Fuel Tank dropped and cleaned/replaced
Fuel Sending Unit/Pickup
Fuel Filter
Oil Change
Spark Plugs
Cap/Rotor
Brakes addressed/flushed....
Tires.
Windshield??
I would lean toward the lower end of my range above especially since you said rust is visible and it doesnt "run".
Period.