Sure, but being "financially responsible" doesn't necessarily mean you can't ever go on a holiday and if you do, it should be to the cheapest crappiest shithole you can find.
It means making sure you don't overextend yourself because of a folly. You've got over a year to save up. If it's a combination sister's birthday gift, birthday gift for yourself, and your yearly holiday, can you or can't you set aside $20 a week to save up for it, without having to resort to something like "ramen every day", or "well, guess the baby doesn't
need clean diapers every day..."? If it would, legitimately, put you or a loved one in harm's way (not going to the doctor when you should), you shouldn't go - even if it was a once-in-a-lifetime unique opportunity to go on a cruise to Mars.
If you can make it (barring unforeseen disasters), then you really should accept that, once in a while, it's ok to loosen up, and weigh the pro's and cons of this specific cruise.
(If you get a once-in-a-lifetime-cruise-to-Mars-chance and you don't want it, remember me, 'kay?
)
(If you smoke, you can
easily afford this cruise by making it the "reason to stop" if you're enthused by the cruise. Just saying)