That car does not look so bad to me. A car in this state is always carries risk, it is very hard to tell what is missing and you'll have to make extra effort to figure out how to put it together. The pictures could be better, some closeups of the side rails, rocker panels, and floors might clarify the rust situation. I would ask for better photos before I decided -- or find someone to take a trip to see it in person.
Healey's aren't so terribly complicated and it's not that hard to find one nearby to help you see how to put it together.
I think $5000. would be a good price for it if it is actually as described. $8500 sounds high when you consider the risk of the parts that are bound to be missing. If this were a rolling, completely assembled car in similar condition, I think $8500 would be reasonable.
Good luck, I would love to see this one back on the road. It deserves a good home to get it back together before it fades into Healey history.....
Bill
Albuqurque, NM