We currently have a moisture issue in our basement and are looking for a DIY fix.
Our solution is to use an Arduino DHT22 Humidity Sensor and a fan. This sensor cost about $9.50, which is one of the cheaper humidity sensors out there. For right now we are just prototyping a small desktop version so we bought a tiny fan for about $3 as well.
We already had an older Arduino Duemilanove lying around, but almost any Arduino like the Uno will work. The last 3 items we needed were a 10k resistor, breadboard and hookup wires.
Here is our current setup.
In the Fritzing image (the bottom one) we used a speaker image as we couldn't find a fan. Left to right with the sensor face up, pin 1 goes to +5 v. Pin 2 has the 10k resistor going to +5V and also a hookup wire going to digital pin 2. Pin 3 is not used and pin 4 is connected to ground.
The fan's red wire is connected to digital pin 3 and the black wire to ground.
To connect this all in a more permanent solution, we will eventually solder the sensor and wires onto a perfboard and put it inside a plastic project case.
Then we would buy a PowerSwitch Tail II and plug a much larger box fan into it.
What the Powerswitch Tail allows you to do is turn a high voltage device on and off without any worries of messing with mains electricity.