Finding a starting location for your school...

This is what we've experienced:

• If you want flexible terms, the best time to negotiate is during a horrible real estate downturn.
• Being that we're initially interested in daily rental, but at a somewhat prestigious building, it was best to talk to the property manager, not the real estate agent. 
• The real estate agent just wants to make a commission. He has no vested interest in any side deals you want to make with the building owner himself.
• The building owner/property manager, on the other hand, has 100% interest in making money on unused/unsold space while it's vacant.
• Just walk in and talk to somebody. In a lot of cases, the property manager is onsite and also owns the building. Calling is mostly a waste of time. These days it's so easy to blow somebody off on the phone. If you go in and see somebody in person, you're much more likely to get attention.
• Email should be avoided for the same reason.

Taking these approaches will allow you to obtain a space for a daily/hourly/weekly rental rate at a much lower price than a monthly lease. Be sure to let the property manager know that you have full intention use the space more often (meaning more money for them) as you ramp things up. Also, feel free to toss in a mention about how much you love their building and could see your business permanently housed there if the fit is good.