Charity Flight?

It seems that I can't get a straight answer from any local experts,
so.........
The local school PTO will be hosting a silent auction with donated
items. We have been asked to donate something.
My wife and I where talking about donating an airiel tour of the school
district. Would it violate any FAR's that anyone can think of if the
school takes money for the flight? I would not be taking money in
anyone's name and all related cost would be paid for by me. As far as
I'm concerned it would be like donating a toaster that I went to the
store and bought. What would be the difference if I went out and paid
for a flight to donate, or just donated my time and the planes time and
expense?
Lou