By $60 I assume you mean the initial cost of the Fluval Mini Pressurized CO2 20g kit. The cartridges these come with are NOT refillable and must be bought new for $36.00 (3 Pack). Who knows how long they will last but by the time you've gone through 12 refills, you would have spent enough money to buy a sodastream unit, costing roughly $11 for a refill and likely lasting longer. Yes these units appear to be a good price at first, but the refills make it a very expensive way to get CO2 into your tank.
Joutei, if your fish are that sensitive don't use CO2. I've never had any issues with my DIY CO2 and you can add a gang valve if you'd like to "switch it off" when the lights aren't on.