Look farther north and consider a rental house with the sucky economy.
Littleton/Westford is certainly a good place to start. Although Concord isn't far, you're in a far higher priced town than either the Westford area or Leominster would offer. Chelmsford is probably worth looking into as well. In general, the closer you are to Boston, the more expensive.
Biking: Vietnam in Milford (Rt 495 exit 20) is pretty good. It's sort of geared to the downhill jumping crew these days, but if you go off the property, there are still some good cross country trails. Upton State Forest has tons and tons of marked trails and maps to follow them. There are connectors from these trails going north into Hopkinton that loop around Whitehall Resevoir (where I live). I can easily do a 3 hour ride staying only on trails and crossing a couple roads. From the main entrance, don't forget to cross the road and go maybe 1/8 mile north, then up the big hill on the left. Great trails in there.
If you are into downhill, you probably know about Highland up in Northfield, NH. It's a lift assisted bike place about 2 hours from central Mass.