I did the same thing, we included the resort name, our travel agent, dates of course, and we let them do the rest. I advised my travel agent and she gave me business cards to enclose in the invite. We had 7 couples join us and all but one couple used out travel agent. I think we all paid about the same. If you want to email me at firstname.lastname@example.org I will send you what we sent out.
We did not send the destination invites to everyone. We did send an announcement after we were married, and had a state side reception that did include others we didn't invite to the destination.
I am sending out save the dates first with all the information on it. I am making boarding passes, with the info, I had gotten the idea from another forum I am on, took me a while to figure it out since I am not that handy on the computer but I like the rough copy I made and am actually going to Michaels craft store today to buy the cardstock to print them on. I also have a wedding website where I have included all the information that the guests will need.
We were married Oct 9, 10 at CTI, and the announcements were sent out in Aug 2009, in which I did a double sided 5X8 postcard type where one side included all wedding information, the back included the resort information and our wedding website. On the website it included our newsletter, and great detail about the resort, ceremony, travel plans, etc. Fortnately/Unfortunately I was the travel agent and bride, so that made it easier/harder. In march of 2010, we sent out our actual invitation that included a 4x6 double sided insert that had our registry information on one side and travel information on the other. The costs were always included. For those guests that were actually invited, I mailed a newsletter separately from the invitation that was also posted on the website.