You can fly into Tampa and fly home from Orlando. When you fly into Tampa, you can rent a car. It'll come in handy when sight seeing and it's a 90 minute drive from Tampa to Orlando.
You can create a vacation package by using Expedia or Travelocity where you can book "open jaw flights." That's what it's called when you fly into one airport and fly out another.
When I'm creating a vacation package for my family, I always pick dates that offer the cheapest fares, then I'll book the hotels.
There are several low cost privately owned hotels on the beach between Clearwater Beach and St. Pete Beach. Most are not listed on Expedia or Travelocity. http://www.visitstpeteclearwater.com/
Be aware that the rates for most of these privately owned hotels are for double occupancy and charge an extra $10 per person (that includes children).
Live Beach Cam!
On the drive from the Tampa area to Walt Disney World, there's a great "minor amusement park," called, "Dinosaur World." Dinosaur World is located on Interstate 4, Exit 17 in Plant City, which is just 20 minutes out side of Tampa and on the way to Orlando.
Visitors can see up close, 150 life size models of dinosaurs that once ruled the Earth. Search for authentic fossils in an paleontological setting, walk through a dinosaur museum with everything from dinosaur eggs to raptor claws. At their gift shop, stroll through fossils, dinosaur eggs, educational materials, books, toys, artifacts and more. They even have a playground.
They do not offer food service, but they do allow you to bring a picnic lunch. I do remember that they did have pop machines.