I won't be going, but I have a suggestion or two. I did something like this once before, with a different group.

Pick a hotel. Just PICK one. Make it middle-of-the-road, and reasonably large, at least fifity rooms...it doesn't have to be the Bellagio (expensive) or Luxor and it doesn't have to be Motel 6, either. Get something like Circus-Circus, which while it's at one end of the strip, is moderate in price. Yet it's nice enough that those that want to live in luxury won't feel like they're roughing it. Alternatively, get something that's off the strip a few blocks and stay there. But whatever the case, just PICK ONE, otherwise you'll be back and forth with people that can't be sure they're coming until three weeks before the final date and you'll drive yourself insane.

Just pick a hotel, and tell them that you can guarantee selling some small number of rooms, like about eight to ten. The guys that make up their minds, pay up front and get cash on the table get whatever discount you can get. Those that have to wait until three weeks before the event pay whatever the going rate is. For Gods sake don't try to wangle a discount on 30-40 rooms, you'll go insane with the arrangements and might wind up being responsible for the cash for those that don't fill up.

Also, be warned.... only about half the guys who say they are interested will actually show up. Be Very Careful about up-fronting any money.