Another rough value of thumb for city buses is that they use roughly about 30 l/100 km, which adds about 0,50 €/km, so 2,30 €/km for driver + fuel.
A regular city bus holds about 100 passengers, and an average utilisation figure as averaged across the whole day and all routes might be somewhere around 20 %. So an average of 20 passengers per bus at all times, which means 11.5 cents per kilometre for driver and fuel. Now add-in capital cost for the bus itself, maintenance and other ancillary stuff and unfortunately 25 cents per kilometre isn't all that much all of a sudden.
(If you can read some German, somebody did a more complete modelling of costs at https://prof.bht-berlin.de/fileadmin/prof/jschlaich/200811_F..., and with some assumed fictitious but presumably plausible values ended up at 3,26 €/vehicle-km for a city bus operation in 2008 – and both (driver) pay and fuel have increased above inflation since then.)
I moved here from Istanbul 12 years ago. the progress there was positive in this timeframe while in Randstad it was backwards to be honest. public transportation became more expensive and unreliable. busses are often empty and they seem to compensate this by increasing prices and cutting down the frequency, so it becomes less reliable for people to use it..
my commute to work is 15 km. it's 20 min by car without traffic but post-Covid traffic is so bad that it's 50 mins in average (1 hour+ on Tuesdays). bus is 30 mins with 1 connection but often I miss the connection and wait 15 mins, so it's 45 realistically. both are bad options, so I cycle instead in half an hour with my e-bike. if it's bad weather I take the car because busses are not on time so I can't plan being at the office for a meeting or so. plus, bus is much more expensive than my not so fuel efficient old car. go figure.