Or you could wait till the VFC M4 GBB-R's hit the market (which should be any day now.) In country, they'd cost about $750-$850, is partially WA compatible (mags are proprietary), and if the construction is ANYTHING like VFC's past offerings, it may be the best production M4 GBBR on the market.
Of course, it is still too early to say, but I'd definitely wait on that.
YouTube- RA-TECH VFC M4 GBB review