I mean, there are all kinds. Most hold around a half gallon to a gallon of water. Depending on the model, cleaning is also part of having one but each one is different.
This is the one I have but there are hundreds of sizes and models.
So, cheapest route.. if you have steam heat / heaters in every room; just put water in a pyrex ball on top of the heater.
Assuming that won't work; I use this one: https://www.amazon.com/gp/product/B000O3I2CG/ref=oh_aui_search_detailpage?ie=UTF8&psc=1
Slight above your range;but it works great. It can create a lot of mist; and we use it near the lowest setting available or else our bedroom turns into a very humid rainforest.
It does need to be cleaned routinely and gets pretty disgusting if you don't--I've never had a humidifier that didn't have that problem. Unfortunately I've never had a humidifier that is easy to clean because of nooks and crannies.
I've never had a problem w/ humidifier leaks, though.
This is a crappy mobile link to the one I use. It's made a big difference for me this winter.
SPT SU-4010 Ultrasonic Dual-Mist Warm/Cool Humidifier with Ion Exchange Filter - Blue https://www.amazon.com/dp/B000O3I2CG/ref=cm_sw_r_cp_awd_iteQwb73SQ7D2
Forgot to mention I added a second humidifier to the room. Here are the ones I have:
http://www.amazon.com/Ultrasonic-Dual-Mist-Humidifier-Exchange-Filter/dp/B000O3I2CG
They run on 18/6 schedule with the lights because the also drop the room temperature. Grow room stays between 78-85 F depending on the time of day, humidity around 60-65 percent.
I have this Sunpentown/SPT model. I use it at night in my room, during the winter months.
It has a large enough tank to last all night, or two nights on a lower setting. The motor noise is noticeable, but tolerable - a low-level white noise. The biggest complaint is that on higher settings, it creates a light, powdery coating on many plastic surfaces in the room.