The short answer is: Whatever the market will bear. But that doesn't help you much.

I'd agree with MMario about the per diem plus mileage. You should at least get that.

As to presenting yourself as a student rather than an expert, your workshop participants will think what they will in spite of your efforts to the contrary. Just present what you have, and let it go at that. There is no end to learning. (Isn't that one of the quotes from Solomon?) Let us know how the workshop turned out.
Jim