If you want to look up sources it's better to use the live wikipedia at any rate, since it will be more up to date than this snapshot.
My mirror clocks in at 21 Gb. I'm self hosting so there's no real money cost besides the one-time investment in hardware. A really chap person could probably host this off a raspberry pi attached to something like a Corsair Voyager and serve multiple requests per second.
There's some technical trickiness in actually storing the files in a file system, since most filesystems don't deal well with having millions of files in the same folder. So I've had to build a four-tier directory structure based on the hash of the file name to be able to store the files. They're stored in a structure like 31/444/781/225/foobar.gz.
I did some experiments storing them as BLOBs in a database, but I couldn't get it to work.
The bandwidth usage is pretty inconsequential since most of my pages clock in at just a few kilobytes.
I was actually looking at the footnote links, and those do indeed seem to be missing entirely -- as well as the whole references section. Arguably that's more important than links to "definition" wiki pages, so it forms the basis for the knowledge (vs mostly just definitions).