I am on a limited budget (25K max for f&b) and looking into hotels in Cambridge and South Boston that can accomodate approximately 150-175 people. Can anyone recommend any spaces that are willing to negotiate and could fit within this budget that offer a decent view? Saturday evening in September/October. Thanks!

I've heard that the Cambridge Hyatt will negotiate and can be quite a good deal.  They have a lovely view.  Worth a visit, I think. 

I would also check the Royal Sonesta in Cambridge, though I *think* that may be more expensive. 

Oh also check the Downtown Harvard Club--it's stunning.  I'm not sure what their Saturday minimums are though, b/c I had a Sunday wedding.  Also ask about sponsorship requirements.  I know they extend membership to alums of a few different colleges, but I don't know how event sponsorship works.

Exchange Conference Center in the Seaport District. Lot of reviews on that place on here.
Or really south boston is Venezia on the Water.