Sonic: Buy One 1/4 lb. Burger, Get One FREE Take this coupon to your nearest Sonic Drive-In to get one free 1/4 lb burger with the purchase of one 1/4 lb. burger. Offer valid through Monday, February 28th at participating locations. PinShareTweetYum0 Shares Pssssst... Make sure to follow along with @HappyMoneySaver on Instagram, connect with me on Facebook and pin along with me on Pinterest!. Want all the latest straight to your inbox? get the Happy Money Saver Newsletter straight to your inbox!