Sonic: Half-Price Shakes on June 20th This post may contain affiliate links. Please see my full disclosure policy for details. June 18, 2013 18 Jun Pin0Share0TweetGoogle+0shares This Thursday, June 20th, Sonic Drive-Ins will offer 1/2 price shakes all day long! No coupon is required, just drive up and place your order to get yours! *Offer available at participating locations.