I worked with a teacher from the UK and he had a similar issues he got a new passport in less than 24 hrs, I am not sue of the cost. I was jealous because my passport expired and it took 14 business days to replace it. make sure you keep your old passport if you have a Thai bank account. They don't seem to understand that your passport numbers change (at least in the US they do) and yes he got it at the UK embassy in BKK.