Vegas is always a different animal, since they might throw in so many extras if you have a group and are going to gamble. Any other locations, they would charge you for a big meeting room (if you have exhibits or displays) - same room and room setup for dinner - dinner, any equipment (AV, etc.) if you need it and of course any food or drink. I've been surprised at what it costs just to have bagels, juice and coffee for 300-400 people at a conference. You will want as firm a number as possible, and watch how the contract is written--if numbers are less than expected, or if you need some last minute changes or additions...it can sometimes come back to bite you in the ass.
Think of the program you have planned so you'll know what kind of space you need. One big space for everybody? Breakout rooms for special meetings? You got "theater-style" seating set up or "classroom-type" w/long tables to choose...or "dinner style." The hotel will want to know. Are you gonna charge exhibitors for space/access, to help with total costs, or maybe let them "sponsor" some aspect of the meeting? ...Or maybe not do that at all.
Besides each member's air fare and room, bail money, drinks, food, bail money, gambling money and bail money, what are you going to charge for the meeting itself--even just to help cover costs? You'll want everybody to get some shirts & cr*p, goodie bags of stuff, w/free samples and maybe an event program (have vendors buy ads) for people to take home. Door prizes...etc. too, maybe.
Sorry if I made you regret wanting to take this on. :rofl: If you need help, I will be happy to devote some time to this as well.