Hi Julie, good question! I'm not sure how I would charge for this kind of thing although I lean toward setting a 'day rate' (rather than hourly or by head count)... I would start with something that will at least cover your hourly for the time involved PLUS preparation and of course you want to charge based on value as well.
Is the college charging the attendees?
Ultimately, with this kind of thing you're not selling your time, you're selling your expertise, which I believe is worth more than $XX per hour.
I don't know if this helped at all but I'll be curious to learn how you decide to charge for this. It sounds like fun!