I am restoring a '77 Stingray and I have a seller willing to part with one of the early preamp assemblies dated to around the time of my bass. The problem is neither I nor the seller can find any info about the current going rate $$$? The seller wants to be fair and I don't want to spend more than it's worth, obviously! Combing eBay hasn't helped because it's so rare to see only the preamp for sale. Any advice would be much appreciated?