I see 25 total in the 495 belt: Chelmsford, Dracut, Lowell, Tewksbury, Andover, North Andover, Methuen, Lawrence, Haverhill, Groveland, West Newbury, Merrimac, Amesbury. Set to max 500k, houses only. If you include condos there's a lot more.

If you can live farther north and can snag a house in Merrimac/West Newbury/Amesbury, you have easy access to all MA/NH beaches without paying crazy prices, and can be close to some development while still staying more rural. I also really like Haverhill, great food.