I know everyone's version of cheap is different, but go out and hit up your local thrift stores, good used humidifiers for 3 to 10 bucks that will keep a decent size room humid. I got one for 6 bucks, that has a built in digital control and humidity sensor, just set it at the rh you want and it will run until it gets there then turn itself on and off to maintain that level. cheap as it gets as far as I know. if your rh is running between 20 and 45% i think you stated earlier then I wouldn't worry about it, I grow with that rh all the time, no problems, the only time I bother to boost the rh up is with seedlings and the first week or two of veg, after that, they gotta toughen up and send out roots for their water, more roots= stronger plant= more bud, at least in my humble opinion. Even so I do like to have equipment on hand if needed, just in case, humidifiers, dehumidifiers, spare fans, etc. buy them when you find a steal of a bargain, and just set it back, that way when something fails it is a easy fix, no drama, and you don't get stuck buying something when it is at a premium.
