Every time you request something in the shop, the original price increases. price/2=new price+original price
Say a item costs 500 points. After a purchase, we will divide the price by 2 500/2 = 250. Now take 500 + 250 = 750. That will be the new price.
Now, if we took 750/2, we'd get 375. 750 + 375 = 1125. That is the new price.