I would not build the upper , only the lower . There will be less tools to buy . If your a handy guy or your friends are you most likely have the tools to build the lower already .
As for the parts . I agree PSA has the best prices and great quality .
stripped blem lower $60 ( 99% of reviews say they can't even see the blemish) Out of stock now but they have them all the time
Complete LPK including Magpul MOE stock & buffer tube $145
Complete upper /minus BCG & charging handle $319
BCG & handle $170
Total $700 not including shipping add $50-ish
This rifle would be just as good as any sub 1k rifle out there and better then many if not most . If you have some time you can wait for all this stuff to go on sale . I often see these very same items on sale . I've seen the uppers for $279 the LPK for $129 the BCG for $119 and thats $100 less so if you take your time you can build a complete AR for just over $600
I did this AR build in the same way as the above for $600 and this one does not have the Magpul furnture