If your vacation is going to be more than one day, I agree with USA_flyer. Get yourself a good radar detector and you can fly down to south florida on the highway -- at least until West Palm where you could pick up traffic depending on time of day. It is model season in South Beach - and generally will be nice weather.

Not sure what upper limit of not too expensive is for Orlando... my old company had a rate at the Hilton Garden Inn on International drive near $70/night. I think you can get close to that with a pre-purchase Internet or AAA rates - otherwise it runs a little more. Not a resort like some of the options there, but as with most Garden Inns it was relatively new, nice enough rooms, and free internet.