Questions about a/c stuff on a 74 GMC

[1974ChevyC10]

Tomorrow im going to be looking at a complete a/c system out of a 74 GMC a buddy of mine is selling.he is taking everything off the firewall,the compressor and hard lines,reciever drier,condensor and all other necessary components for a factory 70's a/c system.what im trying to find out is what is good price to offer for it since he isnt sure how much he wants and i would imagine used a/c stuff cant be worth a whole lot of money.moderators i hope im not violating the rules by asking this im not selling this stuff myself nor am i helping sell this stuff im looking to buy it for my own use and im not sure what kind of offer to make.if it becomes a big deal for this posting on here then go ahead and delete it.