Cost of prescription for skin whitening medication

I went to the newly opened dermatology clinic for a consultation about melasma, had my face photographed with a special camera, and listened to the doctor's explanation. While I was there, I also got Botox injections on my forehead and glabella. Melasma laser treatment is very expensive, so I only received a prescription for oral medication, which was for a month. When I paid at the end, I was shocked to hear the prescription cost 40,000 won. I wonder if other places charge the same... The unexpected amount makes me feel uneasy on my way back home.

How much is the usual prescription for skin lightening medication?