Definitely stay in Cambridge, though. To get cheap living on the Boston side you have to live way out on the Green Line, which will make it a royal pain to get to meetups and other technology events.
I am in Dallas right now wrapping up Tech Wildcatters, but I'll be back in Boston in August. Feel free to email me.
You're right on the red line, so it's easy to get out to any of the more active (but more expensive) areas like Harvard Square or Kendall Square (where MIT is + the Cambridge Innovation Center and the upcoming Venture Cafe).
Check out the LJ community: http://community.livejournal.com/davis_square
Central Square has TechStars and several startup offices (e.g. oneforty). Central also has betahouse, the best coworking spot in Cambridge / Boston. And you can find places in Central Square that are similarly cheap. But Central Square is probably a bit less safe.