With the prices of admission to all the major theme parks being around $80-$90 per adult per day, it is well worth spending a few dollars on a couple of good guide books.
There are no guide books that are written solely about SeaWorld or Discovery Cove in Orlando but there are several books on Orlando that have chapters dedicated to SeaWorld and Discovery Cove. Therefore you should probably choose a book based upon what else you plan to do in Florida.
There is also a fascinating book about George Millay, the "Father of the Waterpark Industry".
Note that most guide books are re-published annually so you can often pick up a bargain if you don't mind last year's edition. You won't get the very latest information but you could save yourself quite a bit of money.
Also look out for special deals on most Internet book sites where you can often buy two related books at a special discounted price.