BuyDig offers the SodaStream 1-Liter Carbonated Bottle 3-Pack, model no. 1041300010, for $19.99. Coupon code "YUM" cuts it to $17.99. With free shipping, that's the lowest total price we could find for this quantity by $7, although we saw a 2-pack in December for $14 less. They're BPA-free and are designed for use with SodaStream machines.