1978 SC Targa: What's it Worth?

[mwestboxster]

I was not really looking for a car but stumbled across a 78 SC Targa, Guardsman Red. No one was around to speak with, I was unable start it or give it a real careful look over, but looked clean. Interior looked pretty good. No rust that I could see.
Has 160,000 miles on it. Had a 4 sale but no price.
Realistically, if this car is as clean as I hope it may be and hopefully has service records, what kind of price should I be looking at?
Thanks