How much does a commercial central AC cost installed with electric heart including ducting in 7500 square foot building?

AC depends on a lot of things. It's not as simple as you think. It depends on ceiling height. Sun exposure. Your climate. And part of the cost may include a crane to get air handlers up on the roof. You should consult with some reputable commerical HVAC dealers in your area to create a good workable solution.

AC isn't cheap. The unit for my 1400 sqaure foot house with 9' ceilings is about $7000 and I still have to run the duct work.