For me a 650b randonneur has to be French, although the prices can be extravagant to say the least. Still if you avoid the big named collectibles, Rene Herse and Alex Singer, there are some fine bikes that can be had at a fraction of the cost. I have seen bikes by LeJune and Urago sell for very reasonable prices, less than $500 usd, as a complete bike. There are a handful of Ebay sellers that regularly list these bikes and frames, rhclassics is a good place to start although they tend to offer high end stuff.
I was old school before it was cool