We have hired many mini vans just for us, to travel the 10 hours up and down from Hua Hin to Surin and to the airport's now we find that good reliable thai drivers are not easy to find they are eather crazy poor drivers that dont really have much regard for you or other road users, or they drive to slow on a really long journey.
For us especially now we have a baby paying over the avarage rate for a really nice bus with a good driver is something thats well worth budgeting for as we only come over for a month at a time and the convienance and safety door to door, i think well worth it.
For example you could organize visa runs with some border market shopping thrown, in or Pattaya Bangkok Hua Hin service every two or three days.
I dont really agree with the statement that you would have to pay the local taxi mafia if your business on the serface was a tour operator fronted by thai's and your lower key role was punting your services to farangs friends or in bars etc, i for one would be more enclined to book a farang owned business with the promise of safe FULLY INSURED drivers that will take good care.
Just food for thought Pete, as i dable in courier work and light haulage on my four days off from the docks.
Kendo.

Is Bangkok a place or a nasty injury.......Eric Morcombe.
Proud to be a Southampton FC Fan.