has a few issues. 1) The tires all going to be flat spotted 2) Hopefully the A/C compressor seals have not dryed out. (I would manually rotate the compressor) 3) The pads and rotors will probably be need to be replaced 4) Thermostat may now be frozen due to build up 5) air filters may have mildew or just plain junk on them 6) Battery is probably shot by now.
So anyways I am thinking you have atleast 2K worth of maintance to do the car. So I would offer 2K less than what you purchased it for.
But regardless I am sure the car has a special value for yourself and that may ultimatly drive the price of the car.