I don't understand why price of this book went from 500 to straight 1500

I had to order mistborn the final empire cause recently I have listened about it from many people. So I searched the book and at that time around 29 jan the price of that book was 438 rupees but I was not able to order it as I was waiting for permission from my parents. Since I got the permission now and I checked again on 2 feb and it is like 1138, how? The most weird part is the other two books of this series is still 438 rupees and the whole series set I am getting in 1500. But I don't want to buy the whole series at the moment since I don't know whether I will like it or not and therefore I want to buy the first book only