BCM upper will run you 425-450 with BCG, you can get an upper from RGUNS for 475 ish complete and a lower if you look hard will run you 225-250, Stag or RR so you can get a decent ready to shoot AR for 700, now I'm sure there are whiners that will say no thats too much you can get one for 500, I say put up or shut up because you are not going to get anything new for that money and 315 for a Saiga 223 is a good price, again put up or shut up, show me the link where your going to get one new and cheaper.
I just built my 6th AR, I bought my first 3 complete, Bushmaster XM15-E2S, Colt 6700 and Spike's in a 6.8. You get what you pay for. In fact, Spikes has their M4 lower on sale for 250 this month and it rocks, great trigger for that money and their uppers are 525 so there is one for 775.