If you eat at home, it will cost you A = (ingredients) + (preparation). Preparation means electricity/gas/charcoal for cooking, plus hot water/detergent for washing up etc.
If you eat out at a catering establishment, no matter where you are, it will cost you B = (ingredients) + (preparation) + (staff cost element) + (restaurant profit element).
Now, it's entirely plausible that the cost of ingredients at the catering establishment is going to be greater than the cost of ingredients bought at your local supermarket. Preparation might cost about the same, or possibly less given economies of scale. But you will be faced with the staff cost element and restaurant profit element - no hotel restaurant is run as a charity.
Thus the minimum allowance, where you have no choice in the matter, should surely be (B-A) ?
Of course Pie Command can tuck in whilst airborne to some extent - so the impact on their pockets will be less than it will be for a non-flier. But the impact upon non-fliers is likely to be financially punitive - through absolutely no fault on their part.
Anyway, why isn't there a contract in place to feed the five thousand as we had in Riyadh 1991?
If it's 'field conditions', then ask for some hexamine stoves and compo and start brewing up in mess tins on the restaurant tables.......