Here's some instructions for the Lynx bus which were up to date for this February.
Take a bus to Epcot or MK and then a monorail to TTC.
#50 bus - Leaves the TTC at 18 & 48 after the hour. Returns from Sea World at 09 and 39 after the hour (until 9 pm)
At the TTC, the Lynx stop is located at the far end of the platform. Exiting the monorail or ferryboat, head out of the TTC towards Mk parking and bear left around the gift shop located at the corner. You will then walk straight to TTC bus parking. Stops are marked; the few Disney buses which still service the TTC are nearest. Again, the Lynx stop is to your left at the far end (but its actually very close). More than one Lynx route calls at the TTC stop, so be sure you get on the correct bus (the second will take you out U.S. 192 to Osceola Square Mall!!)
Fare is $1.25. They do accept dollar bills, however, the preferred method is five quarters. You can of course use nickels, and dimes as well. They don't take $5 bills or over.
Tell driver when you board at TTC that you want to go to SeaWorld.
Sea World is about the next stop after the TTC and the trip takes about 20 minutes. The bus route is basically I-4 from Disney (TTC) to the Sea World exit. There may be one or two Lynx bus markers after you exit I-4 but before you turn to pass in front of Sea World itself, but the correct stop will be pretty obvious.
Then walk across the Sea World parking lot!!
For the bus home - cross over and pick up the bus on the OTHER SIDE of the street (on the other corner - Renassaince Hotel driveway is right next to the stop). There should be a sign with Lynx paw prints on it.
Sounds a hassle, but it's actually quite easy. We managed it fine with two young children. It's certainly a lot cheaper!