It might be easy to assume that San Juan, Puerto Rico would be a cheap destination, since it’s not really known as a wealthy place, but unfortunately this is still quite expensive. The location in the Caribbean gives it ideal weather for cold-weather people during winter, so demand is quite high, even away from the beaches.
Hotels in particular are unusually expensive for a Latin American capital city, as are hostel beds. Those who look carefully can find some very cheap one-star hotel rooms, but expect the quality level to be very low. The proper 2-star and above hotels charge resort prices, even during the off season. The good news is that the main tourist zones are quite nice and feel like they are worth the money. Condado has a nice mix of posh and mid-priced, while Isla Verde is much larger and runs a wide spectrum of prices.
Food is also fairly expensive as long as you are in the main tourist zone. Some street-side options can help to keep your overall meal total down, but sit-down meals, especially at hotels, will be more expensive than most of Mexico, by comparison. Drink specials can keep entertainment costs down a bit if you find happy hour deals. Cheap beers are easy to find if you ask around a bit.