One of the most common softwares for making PCBs for DIY, is EAGLE. They have a free version, which can make boards up to 80 x 100 mm. I don't know if they non-commercial clause would come into play, but the paid version is, I believe, $49 for the same size boards. This program also works for Mac and Linux. It does have a learning curve, but it's not too bad and there's lots of tutorials around.

When the board has been designed, there are plenty of cheap board fabrication services, like OSH Park, Seeedstudio or Itead Studio. To make the boards moisture resistant, you have to cover them with some form of coating after soldering, but I don't have any examples of this.