You can buy a complete Stag lower for around $200 from www.eaglefirearms.net, stock included.
Then toss on the upper of your choice, and you're set.
Unfortunately, most folks carrying Stag lowers are backordered now due to a loophole in CA law which has shooters there scrambling to buy certain brands of receivers, Stag being most popular among them.
Just food for thought,
-MV