I have a drinkmate and an adapter hose so I can plug it directly into 5 lb C02 tanks I swap locally so it's really cheap! The only downside is it's super loud while I carbonate the water. I've seen ppl's posts online who have similar set ups but with regulators and stuff which I think would help but I haven't figured out how to do it.

I used to swap my tanks at a local homebrew store for $15 but they closed. A local liquor store swaps tanks for ~$27 so it's still cheaper than buying la Croix but a lot more expensive than before.

For a little while I didn't have a car so I bought a Sparkel beverage machine, which is unique because instead of CO2 canisters it uses two powder packets that you mix together in a chamber. It adds water from a reservoir into the chamber and the resulting chemical reaction produces enough CO2 to circulate through a bottle and carbonate your drink.

And the proprietary powder packets are just citric acid and baking soda, so if you know what your doing (I've forgotten the measurements tbh) you can carbonate for real cheap. You could also carbonate liquids other than water with it and add things like ice or fruit or lemon slices before carbonating.

It's more of a hassle than CO2 tanks though. It's about as involved as a fancy coffee maker, and on rare occasions it would fail due to clogs. I was always able to get it running again and managed to make my money back on it from carbonating tap water. I went back to canned seltzer once I got a new car though.

Others have said it gives the seltzer off flavors as well but I never noticed it except for one time when I think I put too much of one powder in.

I've got the soda stream and I drink about 5 liters a day. They have a subscription plan and you can exchange your cylinders. That's kinda pricey, still cheaper than buying packs of seltzer long term though.

I have a few cylinders still full of gas, but I already purchased this adapter thing for them to refill cylinders myself and will be buying beverage grade gas from a welding company near me. That will make it exponentially cheaper.

I don't typically use flavors, so no recommendations there. But yeah I like this thing a lot tbh

I have found that you don't need nearly the headroom marked on the bottle. I fill it to about 1.5 cm below the flange below the threads.

I have an old model that I can gently press the button to let it pressurize slowly. That way the water doesn't splash up into the valve. The more automatic models may make a mess.

Why do you want less headroom? Because it takes significantly less gas to pressurize that smaller volume. I don't take any data, but the bottles per tank went up as did the water per bottle. YMMV

I had a soda stream but I could never get the flavor to match any of the Polar seltzers I loved so I just went back to drinking Polar.

I have a sodapop (noname Sodastream) and got it directly hooked up to a 6kg CO2 bottle (with an adaptor hose). Works like a charm and lasts 2 plp for ~6 month. Of you have the space I can highly recommend.

Some tips regarding filling off a large tank:

Turn the tank upside down so you get liquid CO2 and open the valve slowly

Freeze the empty bottles so they don't vaporize the CO2 as they fill and you can get a full fill

Weigh the empty bottle and fill to tare + amount on the label or when it warms up it'll blow the pressure release. Its pants-shittingly startling when they blow the seal and it's on the passenger seat of the vehicle you're driving and fills the cabin with CO2 fog.

I bought the glass bottle soda stream 6 months ago. My wallet has thanked me. It's super convenient to be able to just make a bottle of seltzer in 15 seconds whenever I want it. It tastes the same as the canned stuff imo.

I do recommend getting the glass bottle model as I feel that the plastic bottles would get funky over time.

I got a soda stream for Xmas and it has replaced my seltzer buying. I got the basic model one that came with an extra tank so it's gonna be a little bit before I NEED to swap out. No clue yet what the exchange pricing is, but I know target does exchanges. I've been using the bubly variety pack of flavors and I've really been enjoying it. Super easy to use, and the bottles can go in the dishwasher. I tried one of their own brand of "zero sugar" Dr. P soda and it was decent, but I've been trying to stay away from soda in general so it's a once in a while thing. Overall I've been pleased because I was buying a LOT of canned seltzers, so I'm hoping the exchange cost isn't bad. I use it multiple times a day as well.