As others have said, the more upscale the hotel, the more likely it is to charge for in-room WiFi. But as others have also said, most hotels have free WiFi in public areas like their lobby, bar, and restaurant. So here's a tip from a frequent traveler: capture an internet connection in the lobby and take it with you up to your room. As long as you don't close your browser, and unless your room is far from the lobby, you'll have a connection for the next 24 hours or so. After that, you'll probably have to renew the connection in the lobby.
This technique has worked for me on lots of trips!