Yeah there's very high demand now, just look at all the new builds and factory rifle purchases described in this forum over the last few months. Heck, I even bought two complete uppers over the summer. I had two lowers and figured I'd better complete them while I still could. One thing different from the panic buying of 2008-9, prices have stayed much lower. Last time I checked PSA had uppers and BCGs in stock. Good luck finding what you want.
The biggest issue with assembling an AR isn't so much getting the parts together right - it's getting the right parts together.
US Army 1966-69, VFW Life Member, Retired Geek