depends on where you are in mass. There is a place called C.M. Goodrich in Pittsfield, rough bandsawn lumber, kiln dried. A little pricey in lengths, but the shorts aren't too bad for small projects. They regularly have honduras mahogony up to 20 inches wide, 2 inches thick, wide boards of all types, and regular stock. All rough sawn. They also have a full woodworking shop and will plane boards, glue up table tops, make panel doors, turn spindles, etc. I have never used any of those services however.Nice people.
Not too far over the mass border is Hankle Lumber in Hoags Corners NY. Family owned mill. Pretty big place. Acres of lumber. A big barn full of kiln dried hard and softwoods, rough and planed. Priced better than Goodrich, but limited to local woods. If I need hardwood I don't already have, or longer than I have, this is where I usually go. Really nice people, the Hankles. Top quality lumber. One of the only places I have ever purchased surfaced wood that was actually ready to work, and didn't need jointing, additional planing etc.
For the absolute best price on pine or hemlock only, it's New Brittan Log & lumber in East Chatham, or New Lebonon, depends on who you ask. Husband and wife team, one helper. 5 miles from my house. Antique circular mill (late 1800's I would guess)powered by a Detroit. Great prices, great people. Honest hardworking people. I buy 5/4 s4s pine 12 inches wide, 8 feet long for $1.10 a bf. I can't justify milling pine for myself for that, unless it falls down in my yard.
Of course if your not in western mass, none of that matters