advise

[fre1621a]

I need some help in finding the value of my Dad's truck. He passed away a few years ago and we had on offer on it and the family really wants to sell. But I think it's a little low.
The truck is is a 1970 Chevy C10 LWB and is truly a Barn Find/Survivor. Dad had purchased in in Nov of 1969 and did not use any more after '75 or '76. It has a little over 18k miles on it. While it's not perfect, it really is a nice truck and very original down to the plug wires and old bias-ply tires.
So we were offered $10k for it and I've seen values all over the place. I think that it's worth a lot more. But what do you guys think?
Thanks, Fred