Round here that would be considered a lot: not a lot for 3 trips, but a lot to fork out for just one term, especially if you have more than one child.
At my boys' primary I would generally expect to pay no more than £12 in total over the entire year for all extras - trips/activities etc. (When we get theatre groups in and so on the children are not charged.) On top of this are fees for residentials in yrs4-6.
But we live in an area of high deprivation so there are limits on what the school can expect.
For instance next week ds2 is going on a "trip" to the new Youth Gym at the Council Leisure Centre. It's about a mile and they are walking both ways. They have to pay £1 each for the trip.