Bellroth

  A quick web search will show you most of them, try https://www.nstgroup.co.uk just as an example.

These trips are not generally, if ever, arranged by the schools. They are instead arranged by companies that make school trips a big business - hence the trips are expensive. And of course the school doesn't have to opt for the cheapest, they are not paying for it. Overall it would be good to see whatever justification schools have for these outings.  It would also be interesting to know if the schools get some kind of kickback for this.