The ERR stuff has the basic lighting and smoke controls, you can program them for steam or diesel operation. If your PS/3 engine has stuff like operating ditch lights, directional markers, etc. you may have to do extra work and add capability to get those operating.
Pricing is whatever the installer you pick charges, and will be dependent on the extra capability you are looking for. You will have to talk to the specific person that will do the upgrade to find out what the costs will be.