I bought 4" PC fans at Radio Shack, and just cut the receptacle end off an $0.89 extension cord and wired them together. Works nice but $20 for a fan sucks! They do last practically forever and are silent which is nice!
One thing that was great for my Neps was a greenhouse humidistat that had a power cord that the ultrasonic humidifier plugged into (a "piggy back cord"). Place the sensor in the grow chamber and set it at 100%, dial it back until the air is well saturated with fog but not raining and you're done messing around as the temps change at night the humidistat adjusts accordingly.
You can build your own greenhouse humidistat with a standard wall humidistat from Home Depot, and something called a "piggy back extension cord" which allows one item to be plugged into another's power cord and the one controls the other. Just ask for a piggy back power cord at Home Depot or similar shop - get one with a nice long cord. Cut off the extension receptacle - not the piggy back power plug / receptacle! Wire the loose end to the humidistat (on an unmarked power cord of two plastic coated wires the one with a lined pattern is the live (+) wire) and place the setup in the driest part of your terrarium.
A standard household humidistat's only go to 60% RH and for Neps you want 80%+ so find a dry spot, my "sweet spot" was up by the lights as far away from the air input as possible to override the sensor and keep pumping in the wet air from the ultrasonic humidifier (just fill it every day or two, easy as pie, you'll be misting/looking at the plants anyway). Once you get the initial placement plug in the humidifiers cord into the "piggy back" plug and plug the humidistat plug in turn it on and wait an hour or so to see what temp / humidity readings come up as, adjust accordingly til you get the readings you want. Once you get the humidistat placement, mark it and remove it from the grow chamber and cover the wire connections in silicone to secure and water proof it. Once the silicone cures place it back in the grow chamber at the marked spot and send in the fog!
Forget those terrarium/table top fountain foggers, they're fragile and tend to not last very long nor make much fog other than for effect. Get an ultrasonic one from the pharmacy that has a 1-2 gallon water tank on it for $30 and cover the output hole with a hose of a similar diameter (1"-2") and run the hose to your grow area. I have a reef wave timer /power strip thing that I plugged a humidifier into and it keeps an on/off schedule of 30 secs to 2 mins you can get something like that for $20 at the pet shop to play around with if you don't wanna buy a household humidistat and wire it yourself or pay $80 for a prebuilt one from a greenhouse supplier.
Here's the plug I'm talking about: