76' KZ900

I have an opportunity to pick up a 1976 KZ900. Its not completely stock and has an after-market exhaust. It in fair condition but has been in a garage/not started for approx. 10 yrs. What is the bike worth? What would be a fair offer price on the bike? It was macanically sound when the bike was put in storage.

Images would help....

'76 non runner, paint and body dusty but not banged up, no serious surface rust on chain, frame, wheels, tank, etc...
Internal tank not rusted...
Cylinders not seized into position...

$600-$1000 pending some of the issues mentioned I guess...