Not many years ago, Croatia was like the newly discovered alternative to Italy that was less crowded and way cheaper, but things have changed and it’s not terribly cheap anymore. Zagreb is still definitely cheaper than Rome, but now they aren’t very far apart in many respects.
It’s true that the main attractions continue to be either free or fairly cheap, so at least you won’t need to spend a fortune once you arrive, but expenses like transportation can really add up quickly if you aren’t careful. Hotels in Zagreb are still definitely cheaper than similar places in Rome, though during peak summer season they might not seem like bargains. Some Zagreb hostels continue to offer good value to backpacker types, however.
Food and drinks are also cheaper than they are in Italy and yet noticeably more expensive than they were only a few years ago. Unlike many other large European cities, at least it’s not impossible to find modestly priced simple meals. Drink prices aren’t too bad, and there are some happy hour deals around if you look.