Humble Bundle 200AD Judge Dredd and others bundle https://www.humblebundle.com/books/judge-dredd-2000-ad-more-books
I've no idea about 2000AD save that they've something like 2K issues of their comic so this is likely one of the only affordable ways to get a hold of a bunch of these stories. There's up to Volume 5 of the Judge Dredd Casebooks, Zenith, Kingdom, Slaine and more.
The only bundle repeat seems to be Vol. 5 of the "Judge Dredd Complete Case Files". It's not that easy to tell which complete storys are included (especially since I know almost nothing about the 2000 AD universe), but I think "Kingdom", "Absalom", "The Ballad of Halo Jones", "Zenith", "Brink", "Brass Sun", "Age of the Wolf", "Zombo", "Aquila", "Mazeworld" and "Counterfeit Girl" seem to be complete, so that looks pretty good.
Corrections welcome, of course.
2000AD handles canon as it follows: most stories are self contained, but a lot of those can become arcs, and everything is canon. Dredd has aged in real time, and being a sci fi story they have ways to de-age him physically but not mentally. Stories change artists but they do follow the same plot, so to speak. If a story is collected in a book you can assume you'll be able to follow it without feeling you're missing out on something, though. At least it's been like that for me.
I'm not an expert on newer 2000AD, which seems to be the focus of this bundle, but I can say Zenith does appear to be complete. Halo Jones isn't and will never be because Alan Moore abandoned the project due to creator rights problems.