Pennsylvania barn find!!!!

This is what I use to get an idea what is a fair price when making an offer [you don't want to piss them off].http://www.nadaguides.com/Classic-Cars/1965/Plymouth/Barracuda-Formula-S/2-Door-Hardtop/Values

^May not work -6906 low retail
15,562 average retail
23,125 high retail
Depending upon rust, missing, damaged parts and restoration costs I personally would not go more than 3000/3500 $. less if possible, but I'm sure the owner knows what they have and won't accept less than 5-8 grand.
Your call.