Converting a granny flat to a loft!

Hi folks,

I'm looking at a house in Brisbane that has a granny flat underneath the living area which has a height of 2m so it is not legal height. I'm thinking I'd like to rip out the ceiling around this granny flat area to create a "loft style" living room, and add an internal stair case upto the second floor where the kitchen is.

Any idea how costly this might be? Of course I'd need to add railings etc and get an engineer to make sure I'm not ripping out load bearing beams etc but wondering if this was a $20-30k job and not a $100k job.