> I would worry about what happens when they get tired of the expense of it.
Reasonable. You might expect them to be subject to the same entropic forces that condemned the defunct sites they’re archiving.
I’m a bit more bullish on them. They’ve got a stewardship/archivist approach and think of themselves as a library. This isn’t googles “cache” which got dropped the moment it was convenient. The archive is the mission.
One of their thrusts as of late is decentralization (of the archive and the web broadly). I’ve even been to their DWeb Camp twice (perhaps why I’m a partisan!). One philosophy you’ll hear around there and might think about for your case is LOCKSS (lots of copies keeps stuff safe).
Hard drives fail, organizations close, and libraries burn. So make more than one bet.
One last plug — they use, make, and maintain a lot of tools for archiving web sites. There are a lot of details of future proofing they’ve thought through so even if you go DIY check out e.g. WARC (