The Sea world/Busch Gardens Fun card costs $98.90 + tax so is only the same cost as a day in each park, great value even if you have to pay for parking.
You can buy them online, you print off an e-voucher and an order confirmation and get them validated at your first park. We changed ours from 2002 to 2003 ones and they said we will get a full refund of the unused vouchers.
http://commerce.4adventure.com/store...sp?dept_id=203
Before we went I asked Sea World and they said their were no Florida residents specials.