Renting a tux can be fairly reasonable and you won't have to carry it in your luggage if you reserve on board. When you get your cruise doc's there should be a colorful brochure enclosed. Just have measurements taken and contact the supplier listed. You can even rent the shiny black shoes to go with it. There is really no choice in styles maybe in colored vests or ties, as you would have by renting from a local Tuxedo shop. If you wish to have a designer look, then contact good tux rental or men's clothing shops near you for their "cruise tux rental" prices. If you are traveling with a lady, you may wish to discuss this with her and coordinate her evening formal wear. If she is wearing a beaded ensemble, velvet or floor length gown you may strongly consider renting the tux.
I don't know about the other lines but RCCL charges $79 according to thier web site. I will be bringing my own tux on my April/May cruise on RCCL since it is my honeymoon and I decided purchasing beats two rentals.