There is a brand called "Digi-Cabi", quite a lot of models under it. I used a Bossman 30L before, basically is not a smart one. The humidifier motor can only be switched on/off, through a knob. This knob is supposed to be linked to the motor to "sense" the humidity level, but I am pretty sure after testing for a week with it that it does not work with what it should be. The Bossman support is not polite and rude to tell me that the product is not an industrial product so there is basically no support of such to explain to me how it should be operated or work.
A "smart", or what I call a correct version, of a good electronic dry cabinet should automatically switch on the motor to dehumidify the air when the humidity goes out of the level you set it to be (for example you open the door it lets in humidify air in, rises to 70% the motor switch on to dehumidify back to the 50% you set). Anyway the Digi-Cabi I bought is about $150, a 70L one. Big enough for 5-7 lenses, acessories and my neg and slides.