Hotels in Sydney vary in price depending on the area and the quality, as with everywhere. Plus there are hostels around, as mentioned earlier in the thread, which are generally pretty cheap and at least contain a bed of some sort. The drinking age here is 18.
Tommy really is right, though. The only reason we have a semblance of a date for this thing is because Brett bought plane tickets and set the date. Seeing as most of the Aussies here live in Sydney and the meetup is there, they're pretty disorganised as to what is going on, so I doubt anyone could give you a soid answer on questions about details. And any details one person gives you probably will be contradicted by someone else. Plus, in general we're pretty lazy, so things will get organised quickly closer towards the date. I know most people don't know what they're doing next week, let alone in February.