That is not easy.I think it could probably be done while reusing most of the code if there was a current gp invested box that allowed numeric input & the choose a grade was split into current/desired gradethen just did the math so the output under the submit button were changed to something like "Grade 2 Average Laboratory (current 2000 gp) -> desired: Grade 3 Average Laboratory (+3000 gp)" using an example of a grade1 lab ()1000gp with 2000gp already sunk from coin/treasure/whatever.