DeputyDan:I think you should consider who is going on the trip.
At my LDS - some trips are right in line with the do it yourself costs and some have a 4-5 hundred dollar mark up.
The difference "I THINK" is that on the trips with an in line cost - the trip leader/organizer travels as a single i.e. gets the free slot.
On the expensive ones the trip leader takes the girlfriend/wife/kids and you are paying for those extra folks to go free.
At least thats my 2 cents.
At my shop we "bid" on trips. You get so many points throughout the year depending on how many classes you teach. Only get one slot- and if there are multiple room types you get the cheapest ones (ie, you are in the quad on Aggessor), if you want to take a SO they have to pay. If you want a better room, you have to pay the difference. For that reason a lot of our married instructors with diving SOs opt for the cheaper trips.