When you request a transaction you also offer a fee. You get to set the fee. If miners don't like it they don't have to include your transaction, and if that happens your transaction will not get confirmed.
After no more coins are mined, miners will be relying entirely on transaction fees. At that point, competition will show us the real cost (and electricity used) for transactions.
Right now transaction fees are low(er) because miners can offset their costs against the coins that they mine as well.
