thinking of an extension?

Hi, I'm wondering if I can get some advice. We are thinking about the possibility of renovating but have no idea how much it might cost. All I'm really wondering is a ballpark figure..in terms of tens of thousands. We have a smallish 3 bedroom house in outer east Melbourne and would like to:
add a bedroom (this would be the only actual external piece of extension)
convert existing kitchen into small study
create a new kitchen in the current living area (this would be on the opposite side of the building where there is currently no existing plumbing)
open up existing bedroom to create larger living area

I imagine the kitchen would be the biggest expense so I'll give a little more detail. We would need new dishwasher and stove, and could re-use existing sink, fridge etc. We would need new cabinets and benchtops. Obviously new plumbing, electricity and gas connections. All the other plumbing in the house can stay as is.
We would want to knock down a couple of internal walls and add a couple.
We would plan on doing all the tiling, painting ourselves, but would want to hire for pretty much everything else.

Can anyone give me any sort of idea or is this too difficult to do?
Thanks