I added the math to another comment and the electricity cost per transaction should be on the order of 8 dollars per transaction. Part of it is payed by the spread between buying and selling Bitcoins, part of it is payed by the influx of new money keeping the spread narrow. The point is that Bitcoin transactions are not cheap, you are just kind of lucky that other people will pay some of the costs for you right now. But this is obviously not sustainable. If the influx of money stops, miners selling their block rewards to pay for electricity will just drive the price down and you pay all the costs with the spread.
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I added the math to another comment and the electricity cost per transaction should be on the order of 8 dollars per transaction. Part of it is payed by the spread between buying and selling Bitcoins, part of it is payed by the influx of new money keeping the spread narrow. The point is that Bitcoin transactions are not cheap, you are just kind of lucky that other people will pay some of the costs for you right now. But this is obviously not sustainable. If the influx of money stops, miners selling their block rewards to pay for electricity will just drive the price down and you pay all the costs with the spread.