I go to Mallorca quite often and always take a low-cost carrier from either Bristol or one of the big London airports. Not many transatlantic flights go to Bristol but there must be quite a few from Vegas or the US into Heathrow or Gatwick from where you could get another to Palma. We usually use EasyJet (Bristol or Gatwick, not LHR) but there are others (Monarch for example)
EasyJet schedules and fares won't be available for a few months yet but you'll probably get that bit of the trip for around £50 if you book early enough. But even that is a 2 hour flight so with all the usual hassles it will add 4/5 hours to the journey after the long flight from the US.
Mallorca is a lovely island. I don't know if you were thinking of getting there a day before the cruise, but if you do there's a fair bit to see http://www.youtube.com/watch?v=e35Mq0d53v4
although it obviously won't be as hot in Oct/Nov as it appears in that vid (mid-May)
Hope it all works out