This is the parts list to build your own large SodaStream and save 98% vs. the brand name setup. Total cost is ~$150, and should last you a year with regular usage. Refills cost $30. Conversely, a SodaStream is at least $100, only lasts 1-2 months, and also costs $30 per refill.
- 10lb CO2 tank: $50 (buying a used one is fine. You will need to take it to a home brewing store, and they will swap it for a full one for you for ~$30)
- Regulator: $40
- Tubing: $10
- Carbonation cap + ball lock: $16
That's it! Connect them all together. Fill a 2L bottle with water, put it in the fridge until it's cold. Connect to your new setup, turn on the gas, and shake vigorously for about a minute.