Assuming it was simply for soup and sandwiches, in a pub that regularly provides food, 1000 is a rip off. If you walked into a pub and saw a price for soup and sandwiches on the board of €16.50, you'd walk out again.
OP should ask for an itemised bill so she understands what she is paying for. To me, the publican should have been offering a discount on normal prices, given that the OP was bring 50 customers in who would spend money in the pub
She could tell the publican she did not agree to that price. She could say she only asked for one sambo and one soup per person. She could tell the publican either he accepts what she is willing to pay (i.e. gives her a receipt in full settlement) or he can sue her for it and they can fight it out in court in due course.
Of course, if she was there on the day telling them to dish out more stuff she will be in a difficult spot.