Where do you live? What resolution(s) do you want to use? You can of course use Atari/Commodore/Philips etc. CRT monitors from back in the day. In Europe a SCART cable should work for low/medium resolution (maybe some newer TVs have problems though?). Some older LCD monitors can natively display all ST resolutions. There are also converters that can adapt the ST's signals to HDMI or whatever.
There are many threads here discussing all all this. A few of them are: