You can get very high quality vintage derailleurs like the Suntour Vx series which was a very high reliable derailleur, or Shimano 600 series, both of which can be purchased for under $60. You can find high end French stuff like Huret Duopar for under $70 too.

As far as old school stuff being sold by collectors and hoarders demanding high prices, some of that is true but only on the really high end stuff especially the Italian high end stuff, the regular stuff, as I have shown above, is not true. And new school stuff is sold at equally ridiculous prices by price gouging corporations and LBS's! Don't be scared off by a bunch of fear tactics, if you want to restore your old vintage bike to have vintage components then do so, if you want modern stuff then do that as well!