The people who expect to recover their money will actually expect to lose money. Conversely we had a friend who was expecting to write off the entire $40k and ended up making $20k from the dinner and $12k after deducting gown, photography etc.
To be honest I don't understand why newly wed want to have banquet dinner when they can't afford it.
Wedding is two person's business, the couple should thank people for giving face by attending, instead of making people pay for their "own dinner".
To me, if those who are not close to me invite me, I'll just say sorry not free on that day.
Few years ago, I attended the wedding dinner of a rich guy at Raffles City ballroom, more than 100 tables, and only about 3/4 full, but the couple can afford it.