a free tier

Alternatively, you can just host this stuff yourself and never pay. A Pihole is just DNS-filtering. There's a million guides to do this on the internet already. You can also do it more directly with some routers, I run DNS filtering on an ASUS router with the merlin third-party firmware. It's possibly the simplest thing you can host yourself. Like others have pointed out though, it isn't a replacement for uBO. They both complement each other and I would recommend both to people who are able. The one major advantage it has is being able to block some ads in mobile apps. But it cannot block as many in a browser.