Abstract: A method is provided of modifying a hierarchal cost model of a multi-component system over a time period of the model extending from a historical time to a future time, wherein the model is built from item cost indices, each of which is built from one or more commodity price indices created from market data. The model is stored in memory of a computer system that includes a processor, a user input device and a display. The method includes the steps of selecting an item from the model, selecting a time from the model time period (the selected item time), and inputting a user selected cost of the item for the selected time. The processor modifies the item price index to create a custom item price index based on the input item price, the selected item date, and the item's constituent cost indices, and stores the custom price index in the memory. The method may further include modifying the cost model to create a custom cost model based on the custom item price index, and storing the custom cost model in memory.