You could luck out and find a Columbus SL frame that might need major consmetic attention (refinish/repaint) That's the only way you can get them for cheap these days. But that will most likely mean you will lose the bike's graphic identity. Anything above Columbus SL level will be impssible to get cheap unless you are looking at major rust and other potential structural issues.
You can also set your sites a bit lower in the Columbus line and go instead for an Aelle or Tretubi frameset. Except for just a little bit more weight, I suspect that most "mortal" cyclists cannot really feel the difference between those and SL frame's ride. Same goes for the difference between Reynolds 501 and 531 tubing. There's hoards of 80's 501 tubed Peugeot (and a few Gitane) frames and whole bikes out there for the picking.
JMOs

Chombi