Hi Dave & Julie,
Last week I got a taxi from Don Muang airport to Cha-am (approx 20km from Hua-Hin, I think). It was 2800 baht return. That's the official SAFE service. It takes exactly 2 hours.
I can't be bothered arguing these days as the exchange rate is so much in out favour. (It used to be around 38 baht to the pound sterling!)
Plus you get the airport guarantee and receipts.
Hope you have a great holiday
driv.
ps - I have flown to Hua-Hin in the past, there's barely enough time for them to
throw a sandwich at you before you land
I thought that the flights stopped quite a few years ago though.