NADA avg book value....$4525, High book $7025. ..i.e. pristine mint condition, show room new.
These are classic car values, which mean above average condition. Seems that Jeep fits in the category. It doesn't add anything for the extra tops or another set of wheels. So, taking the AVG book price of $4525 and subtract it from the $8500 that he wants for the Jeep. Leaves you $3975, and that is what you are paying for the extra tops and tires.
IMO the price is too high for that Jeep. Myself, I wouldn't go a dime above the $4525, and tell him he can keep his extra tops and tires.
'87 YJ, 4.2L built and bored, 8.5" of lift, 8.8 rear, AX15/NP 231, Tom Woods drive shafts, Flat fenders, 12,000LB winch, Custom bumpers, Rattle can paint job. Never completed...