Quite a few years ago, I purchased for $5.00 a used Rohde & Schwarz SWOB Polyskop III
instrument which comprised a vacuum-tube era sweep generator and a CRT display. IIRC,
it was used as an alignment scope and a SNA of sorts. As might be assumed from the low
purchase price, it came with a few problems.
I contacted R&S about obtaining a schematic and a service manual. Their
asking price was $500.00; after explaining the 100:1 ratio between
the manual and purchase price, I politely declined the purchase.