Cheap and high quality seldom go together in firearms and almost never when it comes to carbines. Most of the civilian copies are hit or miss. The early Universals were ok, most of the rest were junk. Plainfield generally considered the better of the civvies, but hard to find. The Israelis (IMI, IAI?) seemed hit or miss. Same with the new Auto Ordnances. Federal Ordnance made recievers in the sixties that weren't bad, but I haven't seen one in years.
USGI is definitely the way to go, but be prepared to spend some serious coin. Beater grade imports can still be found in the $400 to $500 range. Nice imports will typically be over $500. Non import USGI seem to start about $700 anymore and can climb quickly. For some reason the carbine market really started to over heat about three or four years ago. There are bargains out there, but tough to find.