Be careful your incubator is not sealed too well when closed, the eggs and chicks growing in them need oxygen. Another thing to factor in is when you fill your incubator with eggs those eggs will give off humidity.
I doubt you could buy anything that does that for what you can spend, but monitoring the humidity shouldn't be that much of a bother anyways, in my incubator, which is nothing more than a Styrofoam box with a auto turn, a fan, and heat element inside, I simply squirt some water onto the bottom pan of the incubator through the vent holes, I have been keeping it between 30 and 50% humidity, 50 is actually high for me, usually its 30 to 40 and it stays in that range easily for a couple days, I just make sure to take a peak at the gauge once or twice a day to be sure. After day 18 I am going to boost it up over 60% by filling the water troughs and adding a sponge if necessary.
I am going to see how this hatch goes and the next one I may try dry hatching and adding humidity at day 18.