Sodastream is on sale at a retailer I like, but...

[gulliver]

32. It is about dime a liter

Paid for itself pretty fast. You do have to front for the CO2 tank the first time, but it is exchangeable afterward. One gotcha is that if you wait too long to use up a tank, they'll hit you up with an inspection fee when you exchange it.

I started doing this maybe 10 years ago. At that time, the SodaStream looked like it was going to require me to constantly buy or refill their CO2 containers. I go through about a liter per day on average. So that's a lot of CO2. I ended up getting a 10 lb tank, and it has lasted me probably 4 years and still has a pretty good charge.

Also, I don't think The SodaStream used let you easily decide for yourself how fizzy you want the water. I like it very fizzy. SodaStream may have improved by now.

Good luck!