Amazon has the 12-Count Bang Energy Sugar-Free Energy Drink (Blue Razz, 16oz cans) for $21. Add 3 to cart for $63 - 5% off with Subscribe & Save (can cancel anytime) - $21 off 3 for 2 multibuy discount = $39 with free shipping. Roughly $1.08 per can / 300mg caffine per can. 

• Tip: You can mix / match with these options as well.