Price of 1978 Pontiac Bonneville
just realized that the link doesn't work but it was a 1977 Pontiac Bonneville for $11,000 with 7,990 miles on it. It's also all original with original tires with about 75% tread life left.
Worth $9K tops running and driving/restored if your into those cars. Sounds like you found one in the garage and not started driven for decades. So probably $5K. Original tires mean nothing, I wouldn't run 39 year old tires on the road. Most likely needs a lot of work for sitting so long.