Express passes are much cheaper if you buy them at the park. Chances are they won't be sold out when you get there, you'll be early enough. By the regular pass through NCL and then upgrade at the park, the express through NCL is $140 (if I remember correctly) and you'll save about $40 per person if you just upgrade at the park. It's easy and takes no time at all, you can do it right at the front gate. And the express pass is well worth the money.