I haven't seen any houses being offered for free in my area, but have seen number that were listed at less than $15K USD and wouldn't consider any of them livable without at least some major renovation - and in most cases you'd probably want to just demolish the house completely and build something new. Of course different people might have differing definitions of what is "livable", so your mileage may vary.
Focusing on the abandoned houses is a bit of a red herring, though. There is definitely affordable non-free housing to be found in Japan... less than $100K USD for a move-in ready house in a small city seems very doable to me.
