For archival purposes there already are people working on it. The bigger issue is that there's no flow of new people from IMDb title pages. I can set up my own boards for every movie in IMDb but very few people will find them. It's the sheer scale of IMDb user base that made these boards so useful. With so many total users, even very obscure old movies had a good number of people discussing it.

would IMDB's ToS be OK with this?

but who will pay for the bandwidth?

Why can't there be some project that can take static export of sites and serve them via torrent or IPFS https://github.com/ipfs/ipfs like system. Users who care about this stuff could then pool their bandwidth and storage to keep these things alive, if only in a static form for historical preservation.

how much could a bill like this possibly be per month ?

if people are so interested in keeping the forums, you could try to ask for donations ?

I would guess it's expensive enough to get cut, right? People could donate, sure. It would still need dedicated resources. It's a popular enough service to need high concurrency and reasonably high availability - at least for peak usage, like when the new trailer for the next great trilogy drops.

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