The World Showcase is packed with low to mid price range dining options. There's at least one in every pavilion, and many of them are sit-down options. I know it's not much help in narrowing down your choices, but I recommend that you just walk around the lagoon and pick the spot that looks or smells the best when the time comes. It will give you a bit more freedom to do things at your own pace, and since you're only there for a weekend, that's probably a good thing.
If you're like me and need to plan things to keep from drooling and walking in circles, then I'd recommend trying to get in at Le Cellier. It's mid-ranged as far as prices go, maybe even on the high end of the middle spectrum, but the food is excellent. It's also tough to get reservations there, so the sooner you call the better.