440ml SodaStream Beverage Mix (Starry): 4-Pack $11.48 or 6-Pack $15.75 w/ S&S + Free S&H w/ Prime or $35+

Available:

• 4-Pack $11.48
• 6-Pack $15.75

Both are roughly the same $ / oz. The 4-pack ships more quickly. For reference Target shows the 4-pack as regularly $24.99 and on sale for $19.99.
Edit – just saw this one drop in price as well: 6-Pack 440ml SodaStream Pepsi Beverage Mix $18.05 w/ S&S