What are you talking about?
To get 12 liters of drink, it would cost me about $1/liter with the sodastream. Or $12 total.
To buy the same amount of Monster at Walmart, at $6 for 4 cans, or (roughly) $3/liter, it would take 12 * 3 = $36.
Where is the error, other than my rounding 2 US pints into a liter?
I thought you were talking about a monster brand three-liter soda. I don’t know why anyone would buy 12 liters of soda at a time unless they wanted to bathe in it.