There are three separate costs here - compensation for developing the material, which can be spread over many instances of the course, compensation for the half day or day delivering the material, and the cost of the room and equipment to actually hold the course. I am going to presume you can handle that last one since it will either all be free (on their premises) or you will be paying rental fees for it.
Then when you get a number, sanity check it. If there is similar training available elsewhere, are you cheaper or more expensive (including travel expenses perhaps) and by how much? You may realize that what you need to charge is double or triple (per person) what the big firms charge, because they hang on until they have large class sizes, they amortize development across many more instances, and they can even negotiate cheaper room and equipment costs. At that point you will have to decide whether you want to charge your full daily rate or settle for somewhat less as a way to establish yourself in the training community or with this client or something.