I would suggest having the corporation pay a percentage but also have the employees pay a nominal portion also, there’s something about paying for things yourself that motivates!
As for what to charge, it depends on the time you put into it and how much money you want to make per hour. What is the minimum you need to make?
Since this is not one on one training, you need to price it as a group exercise class, per person.
I also agree with LaRue, make sure you have a minimum person requirement, unless the corporation is willing to pay you regardless.