I have the Emil fleetstar mod installed and all upgrades are a buck. This effects the upgrades on the normal fleetstar as well they are all also a buck. And some of the upgrades like engine are available on the normal fleetstar too! This problem is present on other trucks too where modded truck upgrades affect normal truck upgrades.
Mods upgrades on normal trucks PTS 7.5
Thats because they don't change the file names(engines, etc.) that they edit and update the xml for the new file name.. its not a bug.