The two calibers you mention (223 & 308) come on different platforms. The 223/5.56 Nato (along with the 300 Blackout a few other caliber choices) are part of the AR-15 platform. The 308 (along with the 260, 243, and several WSSM calibers) are part of the AR-10 platform. As a general rule, whether you are buying or building, the AR-10 will run you about $400 more than a similarly equipped AR-15.
I own a couple of these units and they are fun to shoot. However, I do not use them for home defense. The 223 will blow right through an 8" tree trunk. Can you imagine how much drywall and studs a round would blow through before stopping? It is a round that is difficult to control inside the house and would leave it looking like Swiss cheese. Even the lowly .22 cal will penetrate completely through four 2x4 studs stacked back-to-back at close range. My personal choice for home defense is a short-barreled (18.5") Rem 870 with BBB lead shot.
As for the purchase of the AR-15, they are pretty expensive right now (nearly double). If it were me, I would wait for the panic buying to stop and for prices to come back down. I don't see wide support for a full-out ban on "black rifles" in Congress. What may be more likely is a ban on high capacity magazines. Of course, my thoughts are skewed because I already have a couple AR's. It's a roll of the dice for you, but I would wait and see.