Thierry, the market on those Aussie ESB one sheets had increased quite dramatically over the last little while.
Yes - the seller IS asking to much but $200 to maybe $300 is too low right now (generally).
I just chalk it up to your cheapskate ways
The guy with that ESB poster had / has a few of them, along with a lot of other nice titles like Mad Max & Bullitt. He keeps listing posters under different usernames on ebay, so prob gets a few negs.
I have a rolled ESB, which I reckon is worth about $750. The one listed, maybe $500ish. I think Matt bought one recently for around the $350 mark, but some condition issues from memory. You could probably pick up a daybill on ebay for $2-300 these days, but you'd be hard pressed to win a one sheet for that price.
One of the rarer Aus SW is the Jedi style A light sabre. Haven't seen one for sale in years. A case of if you see it - buy it!