Revealed during ThinkGeek's 2012 CES spectacular, the Inflatable Portal 2 Sentry Turret has all the great features of the real thing, except it doesn't talk, light up, sing, or fire off a ridiculous number of bullets. It will, however, float in a swimming pool, so take that, realism!
From the official product description:
Drastic times call for drastic measures, friends of Science. Aperture Science had to make some cutbacks to the production line when OSHA shut down the main plant. Something about air quality or lead paint in the water pipes. Silly, really. That's what waivers are for. Anyhoo, we can't get you any real, bullet-firing turrets, but we did manage to hijack a pool float factory long enough to make a bunch of these inflatable ones
Now how much would you pay? $24.99? I sure hope so, because that's how much it costs. I'm sure ThinkGeek will let you pay more if your heart is set on it.
Portal 2 Life-Size Inflatable Sentry Turret [ThinkGeek]