Personally, I think it would be cheaper to buy off the EE. At least if you can find an upper you like. Building a lower is pretty cheap if you use stock parts and cheaper if you buy used.
You should be able to find a complete upper with bolt, carrier, and charging handle for $400 unless it has lots of options.
You can buy a new stripped lower and build it for $250+ depending on options.
There is a gun show coming up where you should be able to get a DPMS lower for about $125. Lower parts kit should be about $50. A stock with buffer tube, buffer, and spring can be found used for maybe $50.
If you want a new gun check with the guys at Impact or PM Legal Transfers on ARFCOM and get a quote for a RRA model that you like.