Well, although that is a great choice for decking, it is hardly cheap, and some. like me, would regard it as expensive, but maybe worth it.
A cheaper alternative, and the cheapest I know of, is, of course, treated pine, which can, with the right decking stain, be made to look like Merbau, (or anything else) but will obviously not last as long.
The sad thing is, there is very little available in Australia that you could describe as cheap (although I prefer the term inexpensive, as there are plenty of expensive items available that are cheap in quality). Pallet wood would be the cheapest (potentially free) but it definitely wouldn't last long, then again "long" is very subjective.
The best I can offer is that pallets are fairly ubiquitous if you are prepared to scour the area, and broaden your search area, but there is obviously the law of diminishing returns against you. If you have access to a truck or Ute it makes things easier as you can do it in bulk even if you have to travel, if not you have to break them up in situ, which is not easy, I eventually built a pallet breaker, but not everyone has the means to do so.
It's not easy being cheap, but is morally very satisfying. Good luck!
