Dave, if you look around you can find complete uppers for around $900 with the Bolt Carrier Group and Charging handle. Online private sales like ArmsList is your best bet. There's a seller on my local forum that is selling a complete Spikes Tactical upper with BCG for $900.
Pair that with a complete lower around $400-500 and you are golden.
As others said, "building" (more like assembling to me) AR15's right now is not exactly fun because parts are hard to find or very very expensive. I have orders that have been sitting for 2 weeks that are still not being processed or shipped although they already took my money (VTsupply.com).