A humidifier doesn't help that much for me. I have one in my bedroom that raises the humidity significantly, but more than half my time is spent in other parts of the house, outside, or at work. Bringing one to work is pointless because of the air handling system in the building. The lab next to where I sit runs a couple big, industrial humidifiers 24/7 and they can barely keep the humidity at 30% in a 20x20ft room.
As soon as I leave my humidified bedroom my skin dries out.
Here's a good review of humidifiers:
http://thesweethome.com/reviews/the-best-humidifier/I bought their budget pick, and if I run it all night on full power I can get condensation on the windows in the morning. I measured the watts it consumes, and I can't remember now, but it was low. I think it was 70 watts on the warm mist setting and 36 watts on the cool mist setting?
You can estimate indoor humidity from the outdoor dew point if you aren't using a humidifier. Put the outside dewpoint and inside temperature into a relative humidity calculator. That assumes that you take outside air and heat it up, which is close enough. If the dew point drops below around freezing I start to get uncomfortable. Dew point below zero F starts to approach the dryness of an airplane, which is very dry.
Other things you can do to increase humidity:
-Don't use the vent fan when you shower
-Vent the dryer into the house, if you use a dryer
-Dry your laundry on a drying rack with a fan to speed it up