- Riding bikes. Obviously it is free to ride, but there is an initial expenditure required in either purchasing or renting a bike, all the more reason to borrow one from a friend/relative
- Shooting hoops, throwing a football/baseball/frisbee,etc. These are very low cost activities (buying the ball or even just borrowing it from a friend). Good way to get outside and have some fun
- Hiking. Can't get much more free than this, the only expenses I can think of would be when you want to go to a national park or forest and then you would end up paying some entrance fee
- Bowling. Pretty cheap (even after having to rent the clown shoes) and some good old school fun
Some of the pricier ones:
- Golf. This all depends on where you go (wanna play the courses the pros do, then fork over the bucks). Most public courses are reasonable though for the occasional round
- Ice Skating. Not terribly expensive but do need to factor in renting the skates and purchasing an ice ticket
- Water sports (Jet skiing, Water skiing, wake boarding, etc). All a ton of fun, but a little expensive by the time you hire someone take you out in a boat