Price wise it's not too different. It all depends on your hotel. They do not have Animal Kingdom at
Disneyland. That's Disneyworld. The Disneyland resort has the Magic Kingdom and Disney's California Adventure which are sperate parks. I would recomment the park hopper to use both parks. It's very easy to visit both the same day as they're very, very close. It takes roughly 2 minutes to walk from one gate to the other.
The Disneyland Hotel, Paradise Pier, and Grand Californian are all very expensive but do offer easy access to the parks. There are other inexpensive hotels and motels around the area that are within walking distance. Do your homework. Candy Cane and Anaheim Plaza are very good values.
They don't really have a slow season as they try to keep the park full every day. February is their slowest month but it can be crowded for President's Day weekend. Also check park hours since some months have earier closing hours. Disneyland can sometimes close at 8pm (California Adventure 6pm!) during the week so once again research the hours for your trip. These can also change without notice though they usually add hours rather than close earlier.
These boards are a great place for information. Beware of a few people who get angry and pick fights. It's best just to ignore their comments and stick with what the friendly people say.