I second Siesta Key & Yoders but I live a few minutes from Siesta Key and we're locals at Yoder's so I may be a bit bias. (FYI -Yoder's is closed til 9/22 for a remodeling.)Siesta Key beach was recently voted #1 in FL. It really is beautiful. Stay for sunset, if you can, the sunsets here are breathtaking. Locals often hit Captain Curt's just after sunset. It's hole in the wall on the corner of Midnight Pass and the Stikney Point (bridge). The place is a dive but the chowder and grouper are to die for. It's very casual and family friendly.
For cheap things to do in Orlando there are several outlet malls, Old town is fun and free to walk around (rides cost), downtown Disney, City Walk and touring the Disney hotel's come to mind. Animal Kingdom Lodge is a great hotel to tour and you can do a cheap lunch at Mara (food court). My kids also like to go to Disney's Boardwalk at night to watch the free entertainment.