I got it very cheap, $60 including shipping from Europe. However, I lost $80 when the last copy I found in Australia arrived destroyed. Also, I'll probably have it linen-backed and the fold-lines touched up, so that's another $200. (I know the LB haters will protest, but this poster should never have been folded in the first place.) So the real cost will be $350, which is absolutely worth it to me, regardless of its resale value, since it is supremely cool and rare.
A legit international OS copy has never been sold at Heritage or Emovie - they've both mistakenly sold Sonis reprints and video posters as "internationals"- so it's hard to say what it's truly worth. But since the same image is readily available on the US video poster, non-English posters, and UK quads, I wouldn't say it's worth huge $$$.
The Canadian OS is a different story. Dan Rickard sold his for $400 several years ago but I bet it would go for far more if it were properly auctioned.