I think asthetically it will be a tough sell without some loss if you turn around to sell it.
You COULD NOT build that car for 13k if you started from scratch, did it right and bought everything NEW. Not this ' I can throw a car together for $xx.xx with used parts crap'.
I know this, because after tallying up all my spreadsheets and even my CHEAP price I got my SN95 at, I am already over 14k in total cost; and I do ALL the wrenching myself sans paint and tune. Stuff adds up fast. I however think/know I would loose my ass selling it, as I doubt I could get much over 10 or around it just becuase of its milage. That seems to be the cap on these cars or so it seems.
I am assuming, including cost of car, paint, parts and any install/tune fee's he has close to or right at 20k in that car.
If it is worth it to you, buy it. If you are looking to sell it again, either get him down or risk taking an approximate/estimated 3-4k loss. Then again, its up to the buyer.
Just my $.02 worth