For one thing, you don't want to overcharge. While some folks in some of the more posh areas of California may be able to command $250 / month from each student, that's not going to work for most places. You have to look at things, such as the median income, as well as the disposition of the people, for the area.
However, at the same time, you don't want to undercharge. One of the biggest problems is that some folks want to be the lowest priced person in town. While that's a very noble thing, it also might not pay for the lights, water, rent, etc.
Equally important, though, is how much of a value do your clients perceive you to offer? If they believe that you are offering a service that's worth a lot more than what they're paying, then the only person losing out on things would be you.
As sad as it sounds, I've seen excellent teachers have problems keeping a dojo's numbers up, because they weren't charging enough (say, $35 / mo). At the same time, I've seen some truly awful (in terms of skill) teachers keep their dojos packed with students, yet they were charging three times as much as the other guy was charging.
What really irked me, was that the expensive guy kept alluding to his school as the "Cadillac" of the martial arts schools in the area, while putting down the other guy, calling him the "Yugo" of the schools. While that was hardly the case, a lot of times, unfortunately, people will believe this.
Of course, it's not just solely about price. Nobody is going to want to go to a decrepit, rotting building where there are cockroaches on the floor that scurry all over you while you're trying to meditate! However, most folks here want to maintain at least a decent dojo, I'd imagine.