I'm at the Nashua-Merrimack YMCA. They have weights, cardio, spinning, classes, TRX, tennis, racquetball, indoor tracks, basketball, swimming, hockey, pickelball. An adult membership is $50/month. It's definitely not a hardcore gym - lots of people at a very wide variety of levels.

There is a Planet Fitness on 101A and one around exit 6 and one in Merrimack. Bare bones stuff and don't grunt or lift too heavy.

I have a barbell, and a couple of adjustable dumbbells, several fixed dumbbells and a bench at home so I can train at home as well - the weights are all just a lot lower than at the gym.