Diesel, tax, insurance, staff costs, cost of vehicle... all adds up, just it does for cars. Of course there is the operator profit margin too - around 10% - so 16p for your journey.
Hopefully our new Mayor of Greater Manchester will start bringing buses under his control, and help reduce those profit margins. But I wouldn't expect there to be a massive plummet in fares any time soon. Not until our government starts doing something that many other countries do - subsidise fares out of taxes!