Sonic 1/2 Price Shakes All Day June 20I’m sorry you missed this freebie, but please check more Free Samples currently available. Enjoy the official start of summer and treat yourself to a 1/2 Price Shake All Day at Sonic on Thursday, June 20. Plus, many Sonic Drive-Ins are offering 1/2 Price Shakes everyday after 8 pm through the summer! Check with your local SONIC Drive-In for participation.