Jen --
I have the perfect place for you to check out! It's called Marriott Cypress Harbour, and it is affordable villas directly across the street from Sea World. The view outside our balcony was of a tall coaster -- so exciting for the kids!
The resort also has an excellent pool area, beautiful landscaping, great parking, and lots of things to do for the kids. The rooms are magnificent and inexpensive. I would think you can walk easily to the main gate of Sea World because it is so close, and there is easy access to Highway 4, WDW, Margaritavilla, all the usual stuff...
I think they offer Sea World packages, WDW packages, etc. Here is the link:
Orlando Florida hotel near Disney World - Hotel in Orlando by Sea World