6k-8k is my best guess without seeing it, if it runs. Less if there are cracks in the paint near the corners where the front of hood meet the lights. I've seen alot of that on 68's. I think they beefed that fiberglass part up in later years.
This is my wag at it without looking at any kelly blue book numbers or doing any real research.
30k for a perfect 68 #'s matching BB coupe
minus - 10k for not #'s match
minus - 6k for paint
minus - 4k for rust
minus - 2k for interior
minus - 2k for not running
I would buy it and spend like 20k making it the resto-rod it should be.