5 years ago, I picked up the K100D, which was the entry level body at that time, with the kit lens and the 50-200. It was (and still is - I still have it) a very nice and capable set. That was the forerunner of the KX several generations back. The K100 is still very usable and takes great pictures.
As you are finding out, you can go crazy comparing specs and prices in trying to make a decision. Bottom line is the KX would be a professional camera 5 years ago. It does all the essentials and quite a bit more. All the lenses work on it. Same thing with the K20D. A bit over a year ago, just prior to the K7 release, I upgraded to the K20. It too is a wonderful camera.
In the end, the body is less important than the lenses. The KX will do just fine. Here on the forum a lot of folks talk about the newest and greatest equipment. There too are an awful lot of folks still using the *ist from well over 5 years ago, managing just fine. That should tell you something.
The object here is to take pictures while you are away. Weather Resistance is great, but do you really need it. I do not think so. I spent 2 years out at sea on a tin can (destroyer), bouncing all over, seeing the world through a porthole. Take good care of the equipment, do not bump it, keep it dry and if in a humid condition - descant packs work very well. Wrap it in a towel and keep it secure in a drawer (it can get rough out at sea, at times).
You are going to also need memory cards and while you are out working on the cruise ship, you will probably need some place to store your images (a netbook ~ $300, works very well). You will want batteries and at least 2 spare memory cards, along with a little rubber blower to clean the sensor - all pretty minor items in terms of expenses. Then a backpack to haul everything around when you pull in to port (and do not make it look like an expensive camera backpack that yells - come steal me to all the "hey Joes" down at the piers).
So regardless of what system you select (Pentax or Oly), you need to keep your eye on the total system - everything you will need. Also, you are going to want to get it a bit before you leave so that you can test everything out and use it a bit, just in case something needs to be exchanged.
Remember to have fun and enjoy the experience.
hope that helps...