You can already set the price for each tool by going to Edit Process Settings > Other tab, and chaining the values in the "Filament properties" section. Make sure to select the correct extruder in the "Extruder to Edit" drop down first before you change the values.
If you want to have different values assigned to each extruder for different materials, then click the "..." button to the right of the "Save as New" button, choose "Assign settings to categories", search for "filament price" and then change that to the Material auto-configure category.