If you are looking for decent shooter example of a US M1 Carbine then the Israeli surplus carbines at Epps are a reasonable deal. They show a mix of GI parts, and seem to have been taken care of.
Take a close look when choosing one though. Some of the ones with Type 2 rear sights (milled / adjustable) have the windage knob ground down and the rear aperture is spot welded to the 100 yard position.
Although they may not necessarily be considered a collectible, they are great example for someone looking to try out a neat firearm.