There are some on Ebay (search for NesLab). *Probably more money than you want to spend. *It's definitely not the cheapest way to do what you're trying to do.
Unless you're trying to reach ultrahighland temperatures, if you live in an air-conditioned house, simple evaporative cooling should be adequate.
Taking air to be a diatomic, ideal gas, and making a bunch of other assumptions, i estimate that to decrease the temperature 8*C from an initial temperature of 20*C and relative humidity of 30%, you'd have to increase the relative humidity to 80% (relative at 12*C, of course). *That seems to make evaporative cooling a little too effective to my intuition, so maybe i messed up. *But anyway, there ya go. *The point is that evaporation of water is a very effective way to cool something. *Who needs more than 10*C change?
I did, however, not consider the heat added to the water as the ultrasonic humidifier 'atomizes' it. *That will obviously reduce your net cooling somewhat.
If you want to cool the the water first, that will be of some use, but there's really no comparison with the effect you can get from evaporation of water.
Make sure you're not cooling the saturated air after humidifying it... that way you're just putting in work to condense some of the water, instead of cooling it further.