Costco Sale: GoFlav Multi Sport Flavored Mouthguard $9.99 by Rhonda July 24, 2020 *UPDATE* 10/12/14. Costco has the GoFlav Multi Sport Flavored Mouthguard on sale for $9.99 (after manufacturer’s instant rebate), now through October 20, 2014. That is $5 off Costco’s regular price of … 0 FacebookTwitterPinterestEmail