Amazon has the 4-Pack of Red Bull Sugar Free Energy Drink (8.4oz cans) for $5.99 - $1.50 off coupon (check “Save an extra” box, eligible on first S&S order for this product) = $4.19 with free shipping on $35+ or with Prime (extra 10% off for 5+ subscribe and save orders).

Also available in Strawberry Apricot, Coconut Berry, and Blueberry Blue for the same price.