Other costs not already mentioned:
Removal of any solid structures in the back yard you are subdividing off ie. old shed, concrete, trees- $90 per hour to hire a small excuvator plus dumping fees (we had a 7m x 4m shed to get rid of, gave the shed away on Gum Tree, a young couple came and dismantled it, but the trees and contrete base still cost $2500 all up for a bloke to excavate and take to dump).
Puting up a fence along the new boundary line, won't cost much, we did 20m ourselves with $1000 worth of colourbond but it was hard work to DIY.