For Prime members only, Amazon offers the V8 +Energy Drink 8-oz. Sample Can in Pomegranate Blueberry or Orange Pineapple bundled with a $2 Amazon Credit for $2 with free shipping. Assuming you'll spend the credit, that essentially makes this sample can free. (For further comparison, local grocery stores charge about $4 for a 6-pack of 8-oz. cans.)

Note: The credit can only be used towards purchases of select full-size beverages. It's also limited to one credit per sample per customer.