I co-sign the space center, about an hour from Orlando, spend 4-5 hours and back.
If you visit the space center (on Merritt Island just east of Titusville) you could drive south and then east on one of the causeways to Cape Canaveral or Cocoa beach which are on the ocean.
My place is almost an hour closer to these locations than you will be, if you are staying on or near the Disney resorts. From those, Tampa/St Pete are almost as close as the Atlantic coast.