If 10w is your budget and you also expect a 60sqm brick veneer granny flat. Frankly speaking, under current market condition, nobody will do your business.
Add another 2w - 3w, maybe possible. Or you can try to be an owner-builder and subcontract by yourself if you can accept construction period to be 12 months instead of 4 to 6 months.
(I am not builder, I am an owner of a granny flat)
I can't type Chinese on office computer. Just use google translation, the result is so funny especially the last sentence. :-)