I'm from the US, so take this with a grain of salt since I have no idea about laws regarding alcohol locations, etc. I'd look into doing it at an off-peak time at a place where they have lots of space. What about a casino with meeting space? Often there's no demand for that space on a weekend. I'd avoid a workplace boardroom - that's how people get fired. Could you chip in and do a cheap AirBNB for a day/night?