I've noticed the same thing with the prices being the same for a 7 day vs a 3 or 4 day cruise. I'd be interested in knowing what everyone's take is on this. My educated guess would be maybe it has something to do with taxes or port cost's. Maybe these are flat fees no matter how long you go for. I really don't know. I've been on a 3 day cruise (way too short) and a 7 day cruise which might have been just a smidgen too long. The 5 day cruises sound just about right. But I really think even 1 day could make a difference for you and 4 days might be just about perfect. As for the ruins, I haven't been there myself, even though I just came from Mexico. I heard too many mixed reactions about it. The excursion's seemed costly to me and you can't even video tape it without having to pay some sort of fee. They say it's a long ride to get there and there's supposedly a huge mosquito problem. Plus they say it's boring and not worth the money paid (a testimonial from a friend who's just recently been). And that's why we chose to do other things in Mexico. If you're adventurous and like history, maybe that would be perfect for you. In any case, have a great trip, 4 days is only what you make of it. We were on the Enchantment in March, you will love the ship.