where can i buy a complete .22 caliber and .50 beowolf uppe? or is it cheaper and better building the upper

Both can be found at midway

 

22lr

http://www.midwayusa.com/product/717600/dpms-ar-15-a3-flat-top-conversion-upper-assembly-22-long-rifle-1-in-16-twist-16-bull-barrel-chrome-moly-matte-with-free-float-handguard-10-round-magazine

 

50 Beowulf

http://www.midwayusa.com/product/316928/alexander-arms-ar-15-a3-overmatch-upper-assembly-50-beowulf-1-in-19-twist-16-barrel-matte-with-7-round-magazine

 

Both appear to be nj legal, although Im not sure if what the sling loop mounts to on the gas block is also a bayonet lug.

 

As for building them, you might end up breaking even. Usually you can save a little bit of money by shopping the sales on upper parts, but when you pay for the jigs and tools needed for assembly you lose all that savings. If you spread out the tool costs over the 2 uppers you might break even.