We did the Animal park in October and it was tough. I have a 4 and 2 year old. It was a lot of walking! They weren't old enough to do any of the excursions so I wish we would have done Lego Land or the Zoo.
I would check with the hotel you stay at to see if they have deals...they often do. Also, check out the websites of the attractions you want to see. They have some pretty good deals if you buy tickets in advance. If you are a AAA member, you should get a discount too. Also, we can get discounts for a lot of things through our Credit Union.
Also there are deals on the sandiego.org website under coupons for food and other things you may not have even thought of to do while you're in SD.
Have fun!