Gaming Heads is a mini model of the Aperture Sentry Turret. The turret is 16 inches tall (including base and antenna) and features a sound module, which will play samples of the turret's "activation, search, auto search, disabled and tipped over sounds."
The company is only making 350 turrets and they'll be "cast in high quality poly-stone," then painted and finished by hand. Pre-orders are available now and the item will ship in Q4 2012 for $324.99.
We'd mock the price, but then we think about the cost of making a real (or realest yet) Portal Turret with a Penn State education, and now a few hundred dollars doesn't seem so unreasonable.