Here are a few ideas that come to mind...
Campfire songs and Marshmellow roast at Fort Wilderness. It is free and you do not have to be staying on Disney property to go(unless it has changed recently). They have a sing along that is fun and then show a movie outside. You can buy smores kits there or bring your own. They also have a wagon/hay ride there that is pretty cheap per person, worth checking into.
Orlando Science Center is awesome! They have a great planetarium and hands on facility.
Lake Eola downtown. You can walk around the lake, has playground for kids and you can rent paddle boats to go around lake.
Go to the Peabody hotel to watch the famous ducks strut their daily walks.
Take a day trip to Kennedy Space Center in Titusville
Canoeing down Wekiva Springs at State Park. If you are there in the winter months, which by your ticker it looks like you will be, you can go see the manatees at Blue Springs.
I would check out the Budget Board too, I am sure you could get great ideas from some of the folks there too! Good Luck, one thing you won't have is a shortage of things to do in Orlando!
