Originally Posted by Savage25
An alternative if you're going to Hua Hin is to take the shuttle van (~9 or 10 seater) between the Grand Hyatt Erawan Bangkok and the Hyatt Regency Hua Hin. There is a counter inside the Grand Hyatt - IIRC they charge 650 baht each way. You can take airport bus A1 to the Grand Hyatt.
Or these guys charge 590 baht to/from Bangkok or 690 baht to/from the airport at fixed times: 8.30am & 2.30pm
http://www.travel-huahin.com/transfer.htm
Just to follow up as I am back from my trip...
There was an accident in the subway system when we were there. The govt closed the subway system down for a week for inspections and safety checks. Because of that, streets were jammed pack with cars. We ended up taking a the shuttle from the Grand Hyatt because taxi to southern bus terminal would've been a nightmare. It was 500 baht each way. We were the only ones on the shuttle so it felt like a private hire. 2.5 hours and we were there. The driver was nice enough to drop us off at our hotel (25 mins away) as we didn't stay at the Hyatt Regency.
If any of you are interested:
Only one shuttle per day out and return 10am from Grand Hyatt and returning at 2:30pm from the Hyatt Regency.
Just walk up to the main entrance, there's a stall/podium on the right. Tell the person you wish to go to Hua Hin and you are good to go. You pay the driver when he lets you off.