First thing to consider in Thailand is: type of vehicle and usage of it. Cars are "luxury goods" and are taxed accordingly eg. I bought a Subaru XV new in Thailand. Cost around 1.2+m baht and therefore 30% more than the same vehicle in Australia.
Anything with an open bed however (Hilux, Ranger etc) is a different category and is cheaper than Australia by a decent margin, but heavier on fuel of course.
Second hand vehicles of any type are outrageously expensive when compared to home country prices.