Bobbi Lundquist

I noticed today that the exchange rate means 310 Linden Dollars = 1 USD, therefore if I brought 10,000 Lindens that would be $31. I know there is a 10% transaction fee, so change that to $34.10, but the cheapest I can buy 10,000 Linden for is $42.56, a difference of $8.46. They already charge a 10% fee, why do I also lose out on another $8.46 ?, land is expensive as it is, but it appears you have to pay about an extra 25% even after the transaction fee, just to purchase lindens. Please can someone explain this to me