With a water temperature of 50-54F (it bounces around there depending on if the chiller is on or off in the duty cycle), I'm able to get a nighttime temperature of 14C:
My humidity remains surprisingly high, it doesn't seem like I even need any supplemental humidifier.
Although I'll probably set the water temperature to 55-59F to reduce condensation buildup on the outside tubing, which allows me to get around 15C at night.
The power usage is not that bad, the chiller consumes 120W when on, but it's only on maybe 33-50% of the time since it powers off once the water reaches the set temperature. In addition, this system would only be on maybe 8h a day at night, so I'd expect the total kWh to be 0.48kWh a day, which should cost me maybe $1.7 a month.
I can probably further up the efficiency with some additional tubing insulation and also insulating the top. I can probably also reduce the cold-time at night to be maybe 6h instead of 8.
I made a youtube vid documenting my build: https://www.youtube.com/watch?v=RU-9C9Lf0os