Cancún is a 25-mile sliver of white sand on Mexico's Yucatán coast, with calm Caribbean water on one side and a lagoon on the other. December through April is the dry season — humidity drops, rain is rare, and water temperatures sit in the low 80s. It's also peak season, so flights and hotels book out, and prices climb from mid-December through New Year's and again around spring break in March.
For a typical US traveler, a short Cancún trip — say four nights including a mid-range beachfront hotel, round-trip air from a major US hub, and a bit of spending money — lands around $420 all-in. The trick is deciding what to lock in early (flights, the first two nights) and what to leave flexible (excursions, dinners) without paying for it all in one swipe.
One honest caveat: the 0% for 18 months on purchases from date of account opening is a deadline, not free money. If a balance is still on the card when that window closes, the remaining amount starts accruing the standard purchase APR published in the card's terms. Treat the intro period as the date by which the $420 must be gone, and autopay is what gets you there.