Half price Sonic shakes December 21 Dec 192012 Participating Sonic drive-in restaurants are offering shakes for half price. Mention the discount when ordering a frosty treat December 21, which happens to be the Winter Solstice. Thanks to Wichita on the Cheap for the info. Leave a Reply Cancel reply Name (required) E-mail (required) URI Your Comment You may use these HTML tags and attributes: <a href="" title=""> <abbr title=""> <acronym title=""> <b> <blockquote cite=""> <cite> <code> <del datetime=""> <em> <i> <q cite=""> <s> <strike> <strong> Notify me of follow-up comments by email. Notify me of new posts by email.