Hey Mr DB,
Re.."The school i am at gives no break down of the rental costs and fees after a flight. just a lump sum when you return the aircraft."
You are entitled to ask for a breakdown of ALL of the costs presented to you BEFORE you pay, if you wish to.
Normal business practice applies, and your Tax Invoice should reflect ALL costs - with the appropriate GST.
I know of many organisations who 'load' the various landing fees by a small percentage to help offset the cost of administration of same, and whilst I appreciate their reasons for doing so, I do like to know just what I am paying for...and how much.
Cheers