Go out of town to the north, on the right hand side you will see an old petrol station, now a granite and tile shop. Lots of choice.
Cost anywhere between 1800-5000 baht per metre.
It all depends on the quantity, if locally there are a number of granite and marble places approx 10 kilometres north of Hua HIn on Phetkasem road.
If you require large quantities, then I know of a very reasonable place with an office in BKK, and a marble mine near to Saraburi, where you can get marble as cheap as tiles. However they import most of the Granite from China.
John, on the road between Saraburi and Khorat there are a whole load of yards selling various marble and stone products, like you say they mine the stuff in the area and it is as cheap as tiling.
Yes your'e right. I spent some time looking around a lot of those marble shops myself.
I went direct to the marble factory where they extract it from the ground and cut it at the factory. What an exciting day trip I had, and ordered 450 sq metres for my house.
Its easy just to go up the road to the shop and pay top whack !!