3,000 Baht a tree?
There have to be somewhere a mistake in your calculation/estimation:
I do not think that from a rubberwood log could be made more than 2 cft of sawn lumber.
And imagine that the boards 1 - 1.2 m long of width 2", 3", 4" (you hardly get 5"), sawn on thickness 3/4", 1", 1,5", dried and treated by harmless insecticide are sold around 400 Baht/cft.