just use a hand held paper hole punch, if you want to make something good just use an air pump, a med to large size tup or ziplock container, (something you can tape to the walls or that is big enough so the snakes cant tip over) air stone and tubing.
Punch holes in the lid, punch some holes in the top and hang a sponge in the water (hang sponge so part is above water) put the airstone into the container so that is is at the bottom of the container hook up the end of the hose to the air pump turn on the air pump. The air pump will cause air flow over the exposed soaked sponge and evaporate water upping the humidity.
Its a cheap way to do it, also get a back flow guard on the air tubing, cost about 2 bucks so if you turn off the air pump water doesnt flow backward toward pump due to gravity.

I would change the sponge every so often to avoid mildew though.