As a general proposition, hosting a server is not a particularly complicated thing. As I noted, the main thing is knowing how big the data footprint is. The structure is already there, so internal links should translate directly. I don't think there would be a great deal of strain on any server. All we would need is a link that points to the archive, wherever we decide to house it. Yes, there would be dreck that would be transported with it, but that is the price of doing business.
I agree that the main effort should be in maintaining the community that is Reader Rant as an active enterprise (looking ahead) and not having a break is imperative in that effort.
That sounds like a very workable idea...there can be an ARCHIVE section that points offsite from the main server.
And it WOULD be cheap because the amount of use by members would be minimal, like wandering into a reference library reading room to check out an old encyclopedia once every other month.
And yes, ancient discussion threads could be all locked so they are "read-only".
Just fix a hard bar on anything posted prior to the Obama administration years, for example, anything prior to 2008 or 2012 gets archived.
Does that sound reasonable?