Difference in price between timber floor joists or concrete

Hi. I'm planning on building a 2 storey home. It will be a granny self contained unit and double garage downstairs. And a 3 bedroom home on top.
It will be set on a concrete slab but the first floor I'm having a dilemma. Whether to do a concrete floor or the timber floor joists?
It's alot to do with sound for the bottom unit. But what would the price difference be?

You can also consider a hybrid solution, e.g. Speed Floor system (http://speedfloor.com.au/)

I had a situation like that in the first house I built, I had a concrete slab where the garage was, then stepped up to ground floor granny flat on timber joists. Upstairs was the rest of the family home.
For us it made no difference in cost because we were building over a sewer line so a slab under the granny flat would have needed more excavation and concrete bridge over the sewer etc, so costs were similar.
Unless you really need to, just go with slab on ground.