How to make or salvage a humidistat and have it control a device?

I'm using a portable plug-in electric kettle as a humidifier. This is it:


I have a separate little handheld hygrometer, so when I see that my room has reached a good humidity level I have to manually turn off the kettle.

My question is, what is the cheapest way to make a humidistat, even from parts salvaged from other things, and have it control this? I have experience in electronics, circuitry, soldering etc. but I don't know where to begin on this one. I can provide any info such as specs on the kettle if needed. Appreciate any ideas and thoughts!

Well the core of your humidistat is the sensor, which is usually quite an awkward thing.

This device from Honeywell makes it simpler

Farnell/Newark ships internationally.

The rest you could do with an arduino, or something cheaper and simpler with a couple of op-amps. You need to build a comparator with hysteresis like this.

Which I have taken from this excellent site.