The cost is $120 plus tax, you need to book it at 7:00am exactly 90days out. besides CRT...it is almost one of the hardest reservations to secure....call 407-WDW-PLAY
It is a blast...we have done it about 4 times and absolutley love it...hoping ot do it again in december....
Check out the very top of the this board --- the second post is all about the cruise. It has great info and if you want to try to share a cruise, there's links to the next few months where people post about sharing.
We really did like it, although we weren't able to see the pictures projected on the globe as well from the boat. It was very relaxing and we really felt special.