It will be the cost of the coach. Probably can't get a small seater coach, so having to pay cost of full seater. It is because there are only 13 of them, and coaches are usually minimum of about 30 seats (I think, organise some school trips, but have no brain at the moment)
HOWEVER, I think the food teachers at our school would be very interested in a trip to Warburtons!! Where is it? I know it is somewhere North like Lancashire or Yorkshire, so near me
I hate to say this... Each member of staff that is out of school costs about £140 a day. You might find that it is one member of staff and possibly an admin staff member or teaching assistant. Whenever trips are organised, we have to factor in the cost of cover for a teacher for being out of school for the day. There may also be administrative costs. That, plus the coach for the day will probably then meet the cost. Hope that helps a bit.