Can't get that price any more. You are going to pay $50 FFL fee for a $250 complete lower. You upper is going to run you $300 these days. You then have get the expensive ammo. I would go for 7.62x39mm upper for the cheaper ammo.
that's one of the reasons why 300 blackout is so popular...you can use all standard AR-15 parts. The only thing you need is a 300 blackout barrel. You can even use the stock bolt carrier group. Plus it gives you lots of options such as very quiet subsonic rounds all the way to high velocity rifle rounds
if you buy your lower locally you can avoid the transfer fee. I believe Fred's gun shop is still getting lowers in. A friend of mine picked one up from him recently