Seems like a steep price. I'd only get it if the price were talked down, and if both were in minty-new-ish shape. The M1 is "Legendary" and all, but I'd question your motivations for it first:
-- Do you need it for live performance?
-- Do you need it for the sounds?
-- Do you already have any type of midi-compatible keyboard handy?
etc.
Korg has released their entire M1 software footprint, so you could potentially run it on a Mac or PC, and hook up a midi controller to your computer to get the exact same "sounds". For example if you buy a Korg nanoKontrol, they give you that software for free.