Bucket of ice water, mostly ice. Fish tank air pump, pushing air under the water. Bam. Higher humidity, slightly lower temp. (Will help the humidity much more than the temp though)
Assuming you have room for a bucket. 20 plants seems like a lot in that space. I'm sure its a beautiful dog.
Are you sure your room is 65 deg C? That's about 150 deg F. I wouldn't worry about the humidity being that low.
use a plant misting spray to wet the walls in ur space, sounds like you need some ventilation/extraction dude. as an alternative put a couple of low energy bulbs( i use a couple of domestic bedside lamps) in your space and put them on so you can turn your main lights off for an hour or so to allow things to return to somewhere around 30c at canopy height....then you can put your main lights back on and remove the low energy light bulbs....or leave them in there and use a timer to switch between the main and low energy lights every 3-4 hours this will bring your temp down, dont worry about humidity untill you get those temps down. good luck mate peace out G
Turn your lights off immediately. Are any of your plants still alive? I doubt it at that temperature. I don't understand how your temperature could get as high as that, there must be something obviously wrong. I'm guessing your exhaust fan is turned off, so check that first
Air conditioner and fans to air out the room. Following what GoldGrower said assuming your plants are dead humidity shouldn't be a problem. Run a EzCloner to clone new ones and that should raise your humidity significantly