Just about any forged or billet lower will be fine. Brownells (and others) have some “17 Defense” in stock, and an Anderson/Stag/Spike’s are all fine, too. Expect to pay about $70-$100, for now.
You can spend more, but it won’t make it any more reliable or accurate.
Your best “upgrade” will be a $100-$150 Timney/CMC/et al, cassette trigger.
