Amazon has Mountain Dew 12oz cans, 12cs case for $11.25 after clipping $3 off coupon located on product page.
Price for 5+ S&S items will be $9.75 plus tax.
There are also other flavors available with the coupon as well. All for $11.25 after coupon and S&S.
The link above is for the 16oz cans. Price before coupon is still $15. However there is no S&S option.