+1 this idea. In ReplicatorG/Skeinforge you can set the printer's operating cost/hour and the filament's cost/KG, and it'll estimate print time and volume of plastic, and print out a cost estimate for each sliced file. This can be handy if it's the printer is shared, or if you want to keep a sense of the cost of prints. And it's quite convenient that it writes it to a text file next to the gcode, so you automatically generate them all the time, and look at them when needed.
Of course, actual print time depends on the printer's configuration, but even an estimate is useful.
I would guess that if a value can be saved that it gets saved in the XML file. I'd search the XML file for the values. It is possible that the values are there but not actually exposed to the user to change in the user interface. That might be just oversight, I've done that plenty of time on the PLCs I program.
i get the feeling this is a feature that was being worked on but not completed when it was time for the update release. i would suspect all that next update we will see it completed with areas to select currency and cost.