Go to see a local sports group.  The scouts love to watch the games and they enjoy being some place different for the activities.  The trip can cover more than one of the requirements or electives for your scouts.  Many teams will give group discounts if you call the ticket office and set up the trip with them, they may even welcome you to the event over the P.A. system.  The cost of this can get high but can be less if you get end seats.

Go to a Nature center.  Most of these centers have people on staff that can give classes on many areas.  I have taken several groups to classes on everything from trees to edible plants.  The cost of this is little more than snack money and gas.

Go to a local Zoo.  There is a lot to learn at a zoo.  The boys will have a great time and learn a lot.  The trip can also help them get their World Conservation Badge.  If you call ahead you may be able to set up a class from one of the zoologists or an up close meeting with an animal, this can be a bird ( Rapture ) or any one of many smaller animals. 

This may require a tour permit.