Don't know where you're looking but there's plenty available at my gun shops. Also, If you want to slap an upper an lower together at a reasonable price check out DeltaTeamTactical.com.
I got a nice accurate combo in 350 Legend earlier this year. They have all kinds of uppers under $200 and lowers about the same. Just a note, you have to buy a bolt and charging handle when you purchase a lower.