For Prime members only, Amazon offers a Mountain Dew Ice 7.5-oz. Can 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 stores charge about $3 for a 12-pack of 12-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.