I'm trying to make a game that's kind of like buying stocks. The property value / price goes up a random amount over time. You can buy or sell a share for the current value.
Since the prices only ever go up, there needs to be a fee introduced to add risk. I am trying to figure out if the fee should be charged when you buy, when you sell, or both.
I want buying early to be more beneficial than buying later. An increase from 100 to 1100 should be much better than if you bought at 1000 and sold for 2000. Higher prices should have higher risks.
The main problem is that if you buy at 10 then sell for 1010, you make 1000. If you buy at 1000 and sell for 2000, you still make $1000. But it's much rarer for one you buy at 10 to go up 1000 than one already at 2000, so I want to factor in that risk by way of charging fees.
Anyone have any ideas? Sorry if this is too open ended.