@ColinTheMathmo
@icecolbeveridge @Martin_Whitworth @virtuosew
I'll add my tiny voice to this. As a freelancer who is currently (figuratively) beaten and bloody on the floor, even if someone were to offer me a gig with the terms you listed I simply wouldn't be able to accept it because it would leave me out-of-pocket even if I don't consider the time I'd be travelling and working, and I don't have the funds spare to cover the gap.
I understand the point made about it likely being a student-run thing, and not being able to secure the speaker they want is sure to be disappointing, but it may also be an important lesson about the value of people's time and experience.
Also, you've pointed out that this is a "*very* prestigious school"; the implication being that this might be a good reason to give them a freebie. Would you apply the same consideration to an identical offer made by a nondescript inner-city school in a deprived area?