Half Price Cheeseburgers at Sonic – July 21st This post may contain affiliate links. Please see my full disclosure policy for details. July 20, 2016 20 Jul Pin0Share0TweetGoogle+0shares Call a friend and grab a cheeseburger at Sonic tomorrow, July 21st! They will have 1/2 price cheeseburgers all day long!! Remember, these offers are only ever available at participating locations, so you need to ask before you place your order.