Doesn't seem high to me. I recall that my school district replaced the HVAC system while I was in high school and the ROI paid for the new multimillion dollar system in something like 5 years.

http://www.schoolenergysaving.com/schoolEnergyFacts.php

"A mid-sized school district with 800,000 square feet of space pays more than $1M annually for energy."

"Space heating, cooling, and lighting together account for nearly 70% of school total energy use."

That 800,000 sq ft is for an entire district. With a little searching, I found that Saline High School is the single largest school in Michigan at 480,000 sq ft. Most large schools seem to be in the low hundreds of thousands.

So the $100k/mo figure is probably high by a few factors - maybe an order of magnitude at most.

Knock it down an order of magnitude and the payback goes to 100 months versus 360 months on the bonds financing the renovation.

You might have noticed the trend of "de-malling," transforming indoor malls into open air shopping centers. While there are many drivers for this, the ongoing cost HVAC is a big one. So it doesn't surprise me that schools would pay so much.