That's the Shield Tactical "Peace and War Carbine Ejection Port Dust Cover". As for the price, 25 one dollar bills is only about an hour or so supporting single dancing moms, so what the hell. You will need your original spring and pin to install, if you order one. We really like their ABOUT statement on Facebook: [The rules are simple. 'Speak' to people on this page as you would if you were standing in front of them. Keyboard tough guys (and gals) are subject to the boot.]
Go check 'em out on Facebook, https://www.facebook.com/ShieldTactical, and let 'em know the Mad Duo from Kit Up sent ya. You won't get anything out of it, but you'll be doing us a solid. Feel free to join us there as well, https://www.facebook.com/BreachBangClear.