I'm really enjoying flavored seltzer water like La Croix as a healthy alternative to soda. I don't enjoy paying $4-5 a 12 pack. Can you make good flavored seltzer with the soda stream?

If so, is it a prepackaged flavor or is it something I make myself? I have no idea how the machine work but am hoping to get one of it proves to be cheaper than $4/12 pack (which I think it will).