Today only (July 29, 2015), Sonic is offering Half Price Cheeseburger. This offer is valid all day long and no coupon is needed. They do ask that you mention the offer ordering.
Half Price Cheeseburgers includes single-patty SONIC® Cheeseburgers only. Add-ons cost extra. Limit 5. Tax not included. Offer valid on July 29, 2015 only at participating SONIC® Drive-Ins while supplies last.