Ok, I realised that this is a question regularly searched on Google.
I don't actually know how much a Montessori teacher earns, though currently being employed as an Early Childhood Teacher in a Montessori day care on a part basis (meaning less than 38 hours any time in Australian employment terms).
My pay as an Early Childhood Teacher is that as provided by the Industry Award.
However, due to the lack of Montessori trained staff, Montessori schools/day care centres here may/would be willing to hire staff only with Montessori Diploma. The pay rate would be dependent on the category under the Industry Award system, as well as the category that the centre puts you on...
Some of my staff still have to get their locally recognised qualifications by training distance with TAFE to get their Certificates 3, or Diploma. It may not be the most ideal situtation, but from what I know, the staff who did that managed to procure exemptions by half, which is good. (or better than nothing!)