If I were a startup entrepreneur, my third consideration when looking for office space: $$$$$$$.
Of course dollars could probably be numbers 1 through 3, but in my experience there is always a deal to be found, you just need to dig around a bit after figuring out where and what you need. You might be able to find the ideal situation by collaborating with another start up, or hanging out at the Cambridge Innovation Center (CIC) for a while. Or, you might be able to set up in an industrial or flex building that provides the necessary services without the frills of Class A space. You just need to be creative. Just don’t spend money on glass, carpet or finishes.