Just thought I'd share this. I picked up an ultrasonic humidifier at Walgreens for $40 with a $10 mail in rebate. It's 1.2 gallons, seems to work pretty well for me. I have it kick on every hour and twelve minutes for ten minutes (total of 3 hours and 20 minutes a day) and a full tank seems to last at least a few days. Picks the humidity up in my grow rack fairly well and keeps it at around 65% - 75% during the day and around 85% at night. I was able to pick some hosing up at Home Depot and wrap some duct tape around the end of it a couple times to make a snug fit into the output of the humidifier. Some pictures:
You can see at the top where the hose comes up.
Figured I'd share for anyone looking for a cheap humidifier.