You can buy one right now, from The Polargraph Shop!
The Vitamin Kit contains all the unusual / specific things required to build a PolargraphSD machine, and leaves it up to the builder to supply the common stuff: Power supplies, arduinos, cables etc.
The Full Kit contains everything except paper and pens.
What you need:
The setting up your PolargraphSD page is the best place to see what comes in the kit, and how to set it up.
The instructable also gives an overview of what building and set up is like.
Read through it and see if you think you’d be ok with doing it all. Although the kits do contain all the things you need, it isn’t plug-and-play and you will need to do some assembly, and potentially spend a couple of evenings getting it right.