Presently, we could do this job for as little as $50,000; barring any complications with regards to the heating or plumbing-in other words, simple tie ins. This also assuming you have the proper setbacks for an addition this size. Additionally, we're talking four standard windows, (hurricane rated windows cost about 3 x as much) a single door, simple asphalt roofing and composite tile, or comparable flooring. Keep in mind, that this does not include the cost of plans, engineering, electrical upgrades, which may be required or furnace, boiler or septic upgrades. These could potentially add between $5000-$20,000. We are a Wareham based building and remodeling company and I offer this answer based on an actual addition we are doing in the nearby town of Middleboro and one we did recently in Plymouth. Of course, if this is to be a kitchen or bathroom they could add substantially to the cost.