Telex and clearcom are both good gear, however production intercom has some really great stuff for much cheaper then either of the other two, and its fully compatible with both companies. Do you have a sound system in your school? If so, you already have half the job done. Take a mic line that goes to each side of stage and you can run your clearcom line down that instead of pulling new cable. Yes, you will lose an input but I think what you will gain will offset that.
As far the balcony goes, get creative. If you get smaller mic cable, sometimes it can be tucked under
trim, or who knows what else. There is a way to get cable everywhere, you just have to look at every option.