Here's what I use: https://github.com/iamadamdev/bypass-paywalls-chrome

Not available on AMO or Chrome Webstore, unfortunately, but is very easy to install on Firefox, and requires just a bit of effort on Chrome.

I made one for myself a while ago: https://github.com/ImedAdel/arkiv, it just tries to look for an archived version or sends you to a page to build to archive the website.

Not quite perfect, but does the job for me :)