I would also book now so that you know you have a place to stay and, if the prices do go down, you can re-book as long you don't select one of those non-adjustable rates/reservations (make sure to read the fine print). I don't necessarily think prices will go down, but it depends a little on when you're going. The end of June is considered summer season when there are a lot of visitors from away (i.e., needing hotel rooms), and Pixar Pier is slated to open at the end of June. If you're going during Jun 20 to 23, that's when VidCon is happening and that will, most likely, impact hotel/motel availability (and prices).