Private Dining spot in Greater Boston for 25-30 guests?
I clicked on this to reply "Mistral" until I saw affordable! I don't know what their prices for private dining are, but my guess is not affordable. Having planned many private events as part of my last job, I can tell you that you will be surprised at who is affordable, and who is not. One of the last events I planned, we were planning in the Seaport. Legal Harborside was ridiculous with their rules, minimums, room fee etc...Del Frisco's, which I think is one of the most expensive restaurants in town, was far more affordable, better managed, flexible etc. So definitely do your due diligence and call around to a lot of places. Empire, in the seaport has private dining rooms and when eating in there i've seen several parties around your size and they seem to do a wonderful job.
Do you want the $15-$25 to include alcohol? I will be very interested to hear the quotes/ responses that you get.