I disagree with the previous comment. Chan is a restaurant, but a Thai one and the fact that a lot of the staff from the Six Senses eat there is kind of the best recommendation it could get. I myself loved the food there, it was only bettered (for me) by what you can get at Rice Paddy.
In terms of prices, it doesn;t matter where you go in Thailand more often than not there is a price the Thais pay and a higher price that Westerners pay. When you look at what you pay in London, it really doesn't compare!