We are going in 2008 as well. What I did for budgeting is take this year's prices and "pad" them a bit to cover a small increase in prices. I did this when I started planning in 2005 for our 2006 trip and it worked great.
you can book now for april, I am going in june and have booked the hotel, just can't do add on's just yet. you just have to call instead of doing online.