Power Stone Price

[Anthony]

Originally Posted by Lord Morpheus

Do someone knows what happens? Am I doing something wrong?

You're missing "Powerstone prices account for this risk; hence, the true materials cost is divided by 53/54 to the power of P."
The actual cost of a 50 point stone is:
materials: (40 * 50 + 10 * 50 * 50) * (54/53)^50 = 68,745
labor: 20 * 50 = 1,000.
Total 69,745, which inexplicably got rounded to 69,500.

Note that the box on Magic 20 assumes that quirks don't influence the value of powerstones, which is unrealistic, and ignores some more complex math for the actual number of castings required to produce a powerstone.