When we first decided to do this, we still had over a year til the wedding. So we got prices, through my travel agent, from three different vacation companies that do the cruise lines, and once I picked the ship I wanted and the dates we could do, they got us quotes. We went with the cheapest one. Now, they can't do airfare right now but my travel agent, based on similar group trips she has done in the past and it is from here to Orlando, Flordia (so a common group destination), has guesstimated how much the airfare is going to cost. We estimated on the high range. My mom also always makes sure we buy travel insurance so we even told guests an estimate on how much that would cost per person - it is kind of overwhelming but we wanted to make sure people knew how much it would cost them in total - and then they'd have a year to pay it off, which they can make payments through the travel agent.
It was kind of a pain in the butt for me when FI told his Best Man that the trip including airfare and everything would be X price for the best man and his fiancee, which did not include airfare and I kind of busted their bubble after they were psyched about going for that price by telling them wait... theres this.. and this... annnnd this... :s
So I'm putting out save the dates only cause I want to and not cause I have to, since people are pretty much booking already... but I will be sending them to people who are still on the fence and a couple of my coworkers who I would really love to come along.. and I will have a section on there with our travel agents information, and probably give a general price based on double occupancy but if you have a family coming, please contact our travel agent, etc..