I am very impressed that OP's DC can walk 5 miles in an hour.
Is car-sharing with other parents an option?
I may well have same costs as OP in 3 years, just for one year, if DC attend schools in towns 9 miles away, but I don't see it as outrageous. Just a factor to consider.
Life is unfair, we know many people who can't afford (what may be) better state secondaries because they can't afford the bus or train pass.
OP is talking about the £120/month for THREE children, I noticed. Did everyone else get that? This is why children are so expensive.
OP said £2/day, but to get to £120/month for 3 children attending 195 days, each cost needs to be £2.46/day, not £2, no? Are the passes useful for anything else? DS does scout events in the same town as his high school, so saves me that train fare at least.
Is that with a bus pass, NMP? Because if it's without bus pass then what with the odd day off (illness, trips, orthodontist etc), the cost will drop again. And it's only while OP has all 3 DC at that school, not every year OP has any child there.