I don't know about the prices in your area, but I would personally be wary about going to a large group meal like that where we *didn't* pay in advance. I've been to too many meals where someone leaves early and leaves money for the bill that doesn't quite cover what they payed for, or half the people forget to factor in tax and tip when they order and so they give 30% less than they should, or someone orders appetisers that no-one claims, or we split equally, but the organisers decide to order the more expensive options and wine by the bottle, or I end up subsidising the big, tall guys who eat three times as much as I do. Then at the end we sit there until enough people throw in cash so we can leave. It's worth it to me to pay two or three dollars more than I otherwise would to avoid hassle, unless the place will give separate bills.
What are tax and tip options in your area? I'm used to 15% tax and 15% tip, which means that $15 is $11.50 for food, or, if there's a mandatory 20% tip for larger groups, $11 for food - which is fairly good for a meal at a pub.
Now, if the organisers are known for short changing people, that's a different story, and it's probably a good idea just to boycott the event and do your own thing.