Temperature controlled fans-
I've got a set-up like this in mine- maybe it can work for you.
Problem with my terrarium was with all the ballasts & high powered lights in there heat build up would run away... 90F was not uncommon shortly after the light timer(s) came on.
I've got a bunch of 12 volt computer fans laying around... So I decided to use them to cool the terrarium. A 12 volt 1 amp "wall wart" power supply from the thrift store (only a dollar) provides power for the thermal circuit & thus the fans.
I made a thermal fan circuit using this design. It's quite easy to make & the parts aren't too terribly hard to find.
Once that was made I bought a 12 volt relay at Radio Shack which turns off the mist unit when the fans turn on as the new cold (i hope) air will be rather dry. Once the heat has been removed then the mister(s) are allowed to turn back on & 'fix' the humidity.
I'm also using a stripped down 'house' thermostat in the big terrarium- Same setup with the relay & misters as the little terrarium- Difference with this one is the fans come on full power untill the temp drops to a point where the thermostat turns them off. Disadvantage is it can sound like a small turbine engine when the fans are on.
With the thermal circuit the fans gardually spin up as the enviornment gets hotter. It's very quiet.
Seems to work well- Have questions just ask.