There is an all inclusive cpc charge for the Erasable Blue toner. The cost per copy analysis suggests that if on a 60 month lease you do not expect the the customer to erase more than 210,000 pages (3,500 pages per month) you can forget the parts cost and charge the same cpc as for Black at around $0.010 per page with a decent profit.
There is no charge other than the users effort to recycle pages printed with erasable blue.
If a sheet of paper costs $0.010 and Erasable Blue costs $0.010 you can make the case that printing in Erasable Blue is free due to the paper savings. Actually if you were to reuse the same piece of paper three times, it saves your company even more to print in Erasable Blue. Not to mention the reduction in CO2 and water by not using virgin paper all of the time.
It is possible with the built in reporting features of the copier, that a real Eco warrior could track the recycle usage (or lack there of) of fellow employees and send friendly reminders to congratulate or modify their behavior.