Cost absolutely minimal here - I would say:
Uniform - mostly what I would send dd to school in anyway (ie polo shirt + trousers), so no extra cost in buying the right colours. School jumper approx one a year at £7 (but then if she didn't have it she'd need more other jumpers).
Collection plate/silly socks day & the like - maybe one a term at most, usually £1 a time
Fundraising - minimal, maybe one sponsored event a year, and mincepies, concert ticket etc at christmas. Say £20 tops.
School lunch - don't count this as a 'hidden cost', dd has them as its convenient for me, but plenty of children have a packed lunch, so she could take one if the price were an issue.
No charge for trips as yet.
After school activities - perhaps £30 a year for the ones dd has taken part in.
Can't imagine it is more than £100 a year even if you pay up generously for everything and your dc goes to some after school activities. Wouldn't multiply if you had more than one child as you can only go to the school play & eat mincepies once and they're likely to pass on the jumpers!