That's 2007 pricing. I'd say they go for closer to $13,000 +/- $1000.
I would never get into full-auto at today's prices. If I hadn't purchased my AC556 for $2,500 10+ years ago, I would probably have several slide-fire type stocks. Now, I'm considering one of these stocks because my AC556 is becoming too valuable to shoot! I'd rather burn out a $250 barrel or crack a $200 upper receiver than break something on an AC556. Parts kits are going for almost what I paid for the gun - $1,800.