I was wondering this same question. I decided that this is what I would use the 1 year free trial to gauge. That is, run as many courses as possible on the server and presumably the system would report statistics of overall usage. I'd hope you could relate this to the intensity of usage by different classes.
On a technical side, I presume that "6 cents per hour of actual use" refers to system time required to service the page requests. However, I would hope this is the upper bound: 1 year at 365 days at 24 hours = $525.60.