You could eliminate every bit of convention-purchased F&B from a Worldcon's budget and it would bring the cost down -- possibly as much as $5 per member, but probably not that much.
I would like to see some of these people who are convinced that all we do is deliberately waste money and steal it from the poor fans to just try running one themselves. I'm reminded of a Corflu feedback session in which I sat in the back row and listened to a bunch of people who have never hesitated to take shots at "SMOFS" complain about how difficult and expensive it was to put on a 100-person Corflu.
I would also like to be able to organize a Worldcon where that at-the-door membership was commensurate with the cost of other local conventions -- say $125 for five days. (Some of the people complaining about the cost are comparing $50 for two days to a convention that's five days long.) And as soon as I don't have to work for a living and have $500,000 I can afford to risk underwriting half the cost of a modern Worldcon, I'll bid for one.