I use the Bangs feature to open paywalled links with archive.is with !a. When I write !a before the link in the address bar, it redirects to the archive for that particular page. Most of the time it is already in archive.is.

Bang settings:

URL Template: https://archive.is/newest/%s

Bang shortcut: whatever letter you want.

I'm sure a basic browser extension can be developed for that specific action too, but it does not bother me to write !a every now and then.