I think I remember someone else posting that if you call Mears they run some kind of shuttle to Sea World. Disney definitely doesn't run any kind of transportation to Sea World, of course.
As I recall - Mousesavers.com states that you can grab a city bus from the WDW Ticket and Transportation center for $1.25 -- direct to Sea World front gates. (You can grab a bus from Yacht Club to MK -- then hop a monorail to the TTC).
If you wanna save some money, take the Lynx #50 from the TTC to SWF. www.golynx.com for info. Will save you a ton of money, but takes more time. It's your call.