The rate is now $36 per person. I believe you can either book it now, or book it onboard at the Guest Relations desk towards the end of the cruise.
The reason I know the rate is because I'm doing that for my cruise in October, but going both ways. I booked it in advance when I booked the cruise.
2007 - Majesty of the Seas
2009 - Enchantment of the Seas
2010 - Freedom of the Seas