How can I guarantee the purchased price level?

The price level and the price agreements that you agree with one or more suppliers should first and foremost be recorded in a comprehensive Price Level Agreement (PLA). In particular, the monitoring and guaranteeing of the variable price components (depreciation and repair-maintenance-tyres) require periodic checking.
 
Fleet Support has extensive experience of this through drawing up / implementing PLAs and the Lease Rate Monitor as a guarantee tool. This gives you insight into the (in)consistency of the agreements that have been made throughout the duration of your supply contract.