Where can one buy a copy of historical Usenet archives?

I'm looking to get my hands on a copy of historical usenet archives. Mostly interested in comp.* soc.* groups, but anything non-binary would be nice.

1) I'm not sure how big this would be - would it fit on small number of HDDs?

2) are the archives e.g. at https://archive.org/details/usenethistorical reasonably complete, compared to Dejanews/Google Groups?