The alternatives would probably be getting a heat pump to more efficiently use the electricity (but then, the heat pump itself is a lot more expensive than a S19 with watercooling setup)
in a
very round about way i did something like this as a side effect of having a 6 card GPU rig in the basement with an air source heatpump hybrid hot water heater.
GPU rig (~700 watts) -> basement air -> basement air source hybrid hot water heater
bonus is the air source water heaters also dehumidifies my basement, reducing the load on the existing basement dehumidifier. so a a part of the hot water is free as i would have expended some electricity on dehumidifying/cooling anyway.