How about something more cas than having to book a room then? I'd say hey, let's meet at xyz bar on 1/16 and whoever comes comes, and whoever can't can come in the spring (or whenever). But I'm not too sure how young this board goes and how feasible that is.
If Barrymore's (or where ever) is booked - surely there's some lower key restaurant which could accomodate? It may not be in the best locale, so we have to decide if we want to place priority on location or ease of booking.
I haven't ever really planned a large event before - is there something we're missing other than location and people?
"Some of us have it worse, you know, Dana. Some of us are dating lesbian men. Okay? C'mon."