The price online will be the same even if you order on the day you're supposed to leave. The problem, of course, would be that you wouldn't be able to get the tickets on time. The site says that you don't have to pay shipping if you order far enough in advance, but I've never met anyone who got free shipping from online.
I always get my tickets at the Disney Store, which has previously had exactly the same price as Disney.com. I don't know if they've got the 2005 tickets in yet, or if they will continue to carry the tickets next year. The last I heard, they will. But that's hearsay, of course.