You might think about something like laser tag. If he likes video games, it's kind of like being in the video game. I know there's Shadowland out in Gaithersburg--not sure where you are. I think they charge around $20 for 3 games. Obviously rec activities are probably a lot more like real exercise, but maybe this is a way to exercise, burn off some energy, and if you're in school, you can always bring your books and study while he and a friend are in laser tag. I haven't tried it myself--my oldest is only 3, but a lot of the parents at the school where I work love it for a way to burn off excess energy and keep the kids occupied.
In the summer time, there are several water parks around Montgomery County...again not sure where you are. There's a splash park in Gaithersburg that has a splash pool and waterslides...even if you don't live in Gaithersburg, you can still go in, it just costs a few more dollars, but I think it's still under $10 for the day. There's also mini-golf there and a big park. There are a few others like that around Montgomery County but I can't think of where they are off the top of my head.