I'll be visiting this property in a couple weeks but wanted to share some transportation info I received from the hotel for anyone interested in going to Hua Hin from Bangkok:

From the Grand Hyatt Erawan Bankgok to Hyatt Regency Hua Hin:

Arranged by AVIS Counter at both hotels:
Mercedes Benz at cost Baht 4,500 net per car per trip with maximum 4 persons per car

or

Toyota Camry: at cost Baht 3,800 net per car per trip with maximum 4 persons per car

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OR

Shuttle Bus arranged by World Travel Service, counter at both hotels:
550 Baht net per person per way.
Shuttle times:
Departure time from Grand Hyatt Erawan Bangkok: 07.00 a.m. and 3.30 p.m.

Departure time from Hyatt Regency Hua Hin: 08.00 a.m. and 2.00 p.m.