Autofilling Humi for Walk In

Not sure how DIY you are, but you could look into building your own humidifier as well. I couldn't really tell what the Trion 707U uses to vaporize the water, but it's probably something like an Ultrasonic Fogger (Nebulizer). I've used these in Hydroponics as well. They create a fog with a droplet size of 5 microns or less, which is considered 'dry' fog. You can hold your hand in the fog and pull it out and it won't be wet.

This site has a good selection of foggers: Mainland Mart

A single fogger head will run an average of around $30. I don't think a humidor humidifier would need more than that. You don't want to blast the atmosphere with water, just keep the %RH level. They sell little floats for a few bucks that will keep the fogger at the apropriate depth in the water. For a container you could use a 2 or 3 gallon cooler (I'll coin the term: Coolidifier).

With that you will need a humidity switch in between the fogger and the power outlet. Something like This One for around $40. The power to the fogger will stay on until the humidity gets to your set point (70%) and then shut off. If it drops below that, the power will kick back on.

From there you just need to cut a hole in the cooler and attach a small DC Fan to it. It's usually better to have the fan blowing in to the unit, rather than out, unless you have a waterproof fan. So you'd actually need to cut 2 holes in the cooler. One for Input that the fan blows into, and the fog will automatically come out of the output hole. Hook the fan up to the humidity switch as well so it only kicks on when the fogger is running. Fans can be found for less than $10 (Basically the same fans that are used to cool computer cases), and you would just need a DC power supply for it. Match up the power rating of the fan you want with a power supply (i.e. 12VDC @ 500mA). Here's an example of some power supplies: Here

In all you can probably assemble everything for less than $150.

The main fogger units will last for years, but the little nebulizer disks have a 6-12 month life span. If you don't use distilled water, they can burn out in less than a month. They can be replaced for a few dollars each though. That same Mainland Mart site sells the replacement teflon coated disks.

Anyway, just throwing out some other options.