Benk: have you ever complained to the schools about the cost of trips etc. being too high?
I also know someone who literally “bribes” her kids to not go on school trips. So say your kid desperately wants a new bike for example, offer to buy it instead of him going on the school trip. Or perhaps something cheaper like going out for ice-cream one on one with a parent. Whatever works. These trips are generally not mandatory.
And if you’re not in the minority as a struggling parent, try to get the school to have the parents vote (now for next year) on how much they are willing to pay for school trips.
If you’re willing to prepare lunches, you might be able to opt out of the catered lunch cost.
Good luck!