I just go to the dumsters at work and pull them out. When they decomission machines, they are there for the taking.
I have an old one that you can have for $5 plus the cost of shipping, it is either 12"x12" x 4" or by 6". I would have to check. It was installed on my router but I am doing some upgrades and I am upgrading the box with a bigger one that has a nice door. PM me your email and I will send you a pic or 2.
There are many places on the net that sell things like this, just search for electrical enclosures and see what comes up. Radio shack might even have a suitable container, but I am not sure. I prefer an all metal enclosure, but that is just me.