My wife got me a kegerator a couple years ago. It’s amazing! Like $700. Fill up the keg with tap water when you run out (my keg is like 10 gal), refill the CO2 tank every 100 gals or so. I did a math a while back and it’s like 6 cents per glass, not including upfront costs.
Or you can get an adapter to use with a standard CO2 tank with a soda stream machine. Refill those CO2 tanks at your local home brewing supply store, which again is way cheaper than the sodastream CO2