Our KS2 children probably go on 3 or 4 trips a year, day trips, no residentials, so about £5 to £20 a time, depends on whether a coach is needed or if minibuses are needed. Mathletics subscription per year is £5. Children expected to have their own basic equipment, so pencils, pen, calculator, colouring pencils.
Things like individual music lessons, music exams, lamda, mtech, golf, judo, tennis are paid for separately, direct to the teacher concerned, but they are all optional.
All paper type stationery provided by school, so books, exercise books, folders etc...
Uniform is probably the biggest cost, but we have a 2nd hand shop for everything except mouth guards.
We have 2 residentials in yr 7 and 8, a week long each time, but all done as cheaply as possible. Quite a lot of trips in the weeks after common entrance for yr 8, e.g. Tickets and coach to the globe to watch a bit of Shakespeare, tickets and transport to the oval to watch an ODI, minibus to the beach for a day of fun etc...