Mixte values SHOULD reflect construction and material but some people think they have a pot of gold when they don't. I see those $200 mixtes that aren't any different than the Miyata was. Of course they may still be sitting on Craigslist for all I know, and the French ones? You have to deal with the french parts. The better ones also have the downtube shifters rather than the ones on the stem. I think if people wait and search, the right one at the right price will come along. Personally I'm waiting for a Bridgestone with downtube shifters. I did find a Motobecane with those once, at a local flea market for $12. (French but in great shape) Now that was an insane price, I know!
I don't think I've seen one with Campy, but oh, I'd go ahead and pay the premium for that!