On the contrary, I believe you will find that a great degree of the staff involved in the driver experience packages is paid, largely because much of this activity is mid-week when volunteer availability is lowest. The costing should include allowance for paid staff, including payroll burden and appropriate mark-up. The end result will be a fairly pricey package which the British experience suggests will sell. If it doesn't, you really haven't risked a whole lot. If it does, you have utilized idle resources --like the Chama helper engine after it has returned from Cumbres -- and reached a new market segment.
Tom Henry