Right now, your are going to way overpay for on if you can even find one. I'd just periodically look at Palmetto State Armory, Spikes Tactical, Bravo Company, ect's sites. A typical lower goes for $80-$120. Right now, they are going for $200-$300. Just keep an eye on sites like the ones listed. There are hundreds of companies to choose from. Prices will come down, and availability will come back.
I don't know anything about the AR-10s though.
"The greatest danger to American freedom is a government that ignores the Constitution."