I heard october mtn. in pittsfield has about 23 miles of trails. It cost, don't know how much, but could be worth it. Also beartown state forest has legal riding. If you contact the RMV they have a list of state forests in mass were you can ride!

 

You can ride in
Pittsfield State Forest
Savoy State Forest
Beartown State Forest
October Mountain
Tolland State Forest

Sometimes, they might charge you $5 to park, but that's it.

 

Are any of those places good? sandpits? the rockingham trail in NH is ALL whooped out and sux!