If the contractor digs you a pond and you want to keep the soil its nearly about the same price as buying the soil by the truck load.They will dig you a pond for free if you don't want the soil as they make their money by selling the soil.I'm always surprised by the quotes when someone wants a pond dug and the soil kept.I'm sure Coffeecorner can comment on this as he had it done recently. So digging a pond is OK if you want a big pond by your house but then some of you're land is devalued because its now just a pond ( A hole in the ground ).
What guys used to do in Koh Samui was buy land ,raise with soil,wait for the road to be put in ,divide into plots and put a well on each plot and make a good profit by selling the plots off. The only problem with this is your nice quiet house out of town now becomes like living on a small estate.