From my experience of selling my R33 GTST, I stripped of performance parts and sold them seperately
I sold my car for 15K, with custom paint, bodykit, BB hiflow, susp, exh, and 3 peice wheels and stereo
I got another 10-11k for parts I removed
If I had left them all on, I would have been lucky to get 18-19k for the lot
My S2 Stagea is the same, have been thinking about selling when it is finished
Maybe get around 22k for the car with R34 front and body and R34 wheels and will sell all my other parts for 10-12K seperately
I dealt I would get over 32K for the lot
Most people need to borrow the money to buy a car, so in your case, 13-14K is alot easier than 20k to borrow and pay off.