Very simple arithmetic.
Price of raw materials (PBT) : approx. USD 3,000/ton
Price of raw materials (PBT) : approx. 0.3 cent/gram
Weight of each keytop : approx. 1 gram
Weight of 108 ketops : approx. 130 gram
So... Raw material price of one full set is 40 cents.
Now, Retail price of one full set (on amazon.co.jp) is USD 100.-
250 times.. Good for you.
That is a really serious business !!