As someone once told me, something is only worth what someone is willing to pay for it.

In this case I think you will struggle. The poster is far from in good collectors condition, it's not particularly interesting, I don't remember there being any big news headlines from that exhibition and I'd rather spend £30 on a speed controller than a poster as i'm sure many others would.

Sorry to sound so downbeat but I can't see you shifting it easily and you'd be better to throw it on ebay with the other rare robot wars toys that were mass produced and now being sold on.