I've been charged with the job of orchestrating a rehearsal dinner for 50 on a Saturday night in Boston in June. It shouldn't be too formal but can be any cost.
Check out the upstairs at Armani Cafe, it's a great private space. We did a rehearsal dinner there for about 45 people - cocktails and hors d'oeuvres plus dinner. There's a separate bar area, plus room for a seated dinner for at least 50.