You are getting a bit mixed up between under slab piering and installing your poles. There are a few options for doing pole homes on fill, Assuming you can get Machinery onto site. If it's remote then it'll be old school bored piers. Your site class will give you rough depths. Assuming you have less than 6 odd metres to natural, again no big deal. You won't have any load bearing 'slabs' in a pole home so no big expense per a slab on ground.
If you have plans and a site class, the engineering isn't very expensive. I have a couple of good ones in Brisbane if you need recommendations. Until you get your footings detailed no one can guess how much they will be.