...depending on what you consider low cost.

Biking can be fun - but depending on what you want to do, getting the right bikes for everyone can start to get expensive.

Rec passes to the local rec center can take up a lot of time if you've got younger kids who like to swim, etc., but for some families even that is expensive.

There are a lot of fun outdoor games you can do.

Pick up a single GPS unit and do some geocaching. Go explore new trails or locations.