[Im a mediawiki dev]. Typically people use varnish for that use case. MediaWiki does support serving logged out views from a filesystem cache, but varnish is generally a better idea. There are also some caches out of memcached (mediawiki has "parser cache" in memcached which is the part of the page that stays constant between all users. Typically people use varnish on top of that for the entire page for logged out users)

Sometimes people add things to their sites that are incompatible with caching, which will make hosting costs go way up.