$90-$125 seems to be the median range in my area for a commercial dojang. The most expensive TKD dojang I know of charges $160 a month for their Masters Club.
I hear some schools are now in the $175-200+ range. I believe the idea of high tuition came from Stephen Oliver, an instructor in the Denver, Colorado area. He feels that you charge for the value of your services, and if you value what you offer, then you should charge accordingly. I hear he makes a ton of money.