Agree Colin but if Thai dealers are anything like UK ones, they'll bid veery low and sell high (being businessmen and all that!).
Think new ones are 500k or there abouts so I'd hazard a guess at 250 - 280k bearing in mind that it's 9/10 years old. Depends, as "falangs" tend to price a bike on condition/service history, whereas Thais are more interested in how old (older = less £££, never mind FSH). I'm assuming it's a pukka bike with a plate.
Nick, do a search for BMW on www.mocyc.com (in Thai but easy to suss) and you may turn up something there which will give you a guideine.