Let's do a "what if" scenario:

AR's should be pretty easy to convert to Pre-ban rifles for a reasonable fee--change out the barrel and front sight for the threaded bbl and bayo lug, put a collapsable stock on, and you have a pre-ban gun--cost of barrel about $200ish, stock $70ish.  Might even be cheaper to take off the blind pinned muzzle brake and replace the front sight.

Some of the US made AK's could be converted to Downfolders by a good gunsmith (drilling through the receiver for the Downfolder).  The fixed stock milled guns could probably get a side folder (a la Ace) easily enough.

Can you think of any others?

AFARR