I'm also a lefty. The Remington 700 BDL I bought 40+ years ago, in .270 Win, is still a great, good-looking, reliable rifle. Used ones (in a variety of calibers) should not be difficult to find. The sorta good news is that owners of my generation now are dying off and their wives and children are selling the guns. Most left-handed guns are not passed on, due to the shortage of left-handed sons or grandchildren who also want to shoot such rifles. A possible win-win for you.
If I were wanting to buy an AR-style rifle (which I'm not), I'd be tempted to try out a Stag in right-handed, then decide of left-handed is the way to go.