The school may have different packages they offer, perhaps with different hourly rates. The billing system accommodates this using "price groups". The price group defines all the prices you could pay for aircraft hire, flight training and so on. At the top of your Bills & payments tab you should see your current price group shown as a link. Click this link to view the individual prices, which can be set by the school down to each aircraft and each instructor. As an example, the "Standard prices" are shown below:
You cannot switch between price groups yourself, but someone with the office or owner role can do this for you.