Alaska 2010 prices might be out late April-May 2009 if they follow past patterns of releasing.
I would book the cruise/tour through Princess. You have to consider the ease of having the whole package booked through one company. They will be there to guide and assist you the whole way. Look at everything that is included in the land..Hotels, transfers, luggage handling, land tours, entrance fees, transportation by train or motorcoach. Princess' buying power and packaging all the components allows them to offer better pricing than you could do on your own. If you tried to do everything identical to their land package you would be spending so much of your vacation time trying to arrange everything and figuring everything out.
I would sit back and relax, let them do all the work and you enjoy the scenery.