You can pick up a used ball keg, probs $25-30, a cheap regulator, some tubing and a carbonating cap (you can skip the carbonating cap, which last I looked is some $25, just hook the CO2 line to the dip tube, it’ll take longer to reach carbonation saturation, but it works fine), and a hand faucet for $1 and rent a CO2 tank (last time I filled a 5lb cylinder it was $30 which includes the cylinder) and make gallons of the stuff for decreasing spend.
Upfront cost is moderately high, yes thats true, but the more you use it the less it costs per gallon. And no plastic bottles, no questionable water source, no shipping pollution. You just have on demand carbonated water. If you add fruit puree, you can make “Italian soda”, or you can buy the soda syrup businesses and such use if you want, though you’ll want something in a pump bottle and not a box that hooks to a big system..
One 5lb tank of co2 is enough for 5-10 batches, depending how heavily carbonated you like, and each batch is 5 gallons, assuming a standard 1/8 barrel keg, so the math is pretty appealing if carbonated water is a thing you like.