When I had my school I was lucky to find an out of the way spot for $.70/sqft but if you're in a shopping center on a major street it could be upwards of $3/sqft. (maybe more now, it's been a while since I had my spot) In 2000 I was paying $1200/mo rent for a small school in a so-so location. In '98 we were paying over $3500/mo on a BIG place in a major shopping center. Much easier to get walk-in business, but man the rent was hard to keep up with. Then you have insurance and all that fun stuff.
Hope that gives a general idea. But, as I said, these numbers are 10 years old.
There are no PERFECT techniques, only perfect execution for the situation at hand.