I work for costco (not for the travel part, but in a whse). It is sad to say but I have priced a trip through them and seems to be a bit more every time. Not sure with cruises but on land trips is was quite a bit higher.... but never know.. it couldnt hurt to call.. never know where you can find a good deal. I have talked to some who said they have gotten good deals???
I've booked through Costco and received a very good deal on a cruise. They beat everyone's cruise price, including the cruiseline except, CruiseQuick. With them the price was the same. I also found the rep to be very helpful and knowledgeable. When there were price dropped twice she got the credit for me without my having to prompt her. And in the end I was very surprised that I was upgraded (same cabin, higher deck). I haven't used them for a land vacation but I've been looking through their brochure and a couple of items look promising.