Reasonably priced transfers from Airport to Bangkok to Hua Hin to Airport?

My goodness - its such a pain planning a holiday in 5 countries. Can anyone help me to find taxi operators or transfers for our upcoming holiday in Thailand? I have submitted a few enquiries but a) I dont know which ones to trust and b) there doesn't seem to be all that much I can do from Aus. Travel plans are BKK airport to Lebua Hotel to Hua Hin to BKK airport. HELP PLS?