there are two kind of humidifer. the cool one is with a fan blowing at the water which will cool your place a few degrees, this is for summer use and it uses filter. the other one is the warm humidifer that heat up the water to make steam. this will also heat up your room a few degree higher; it is for the winter.
cool one is cheaper, the warm one is around $40+.
i guess i just answer your question.