Well 7m*3m for the last section I got done, that was around $2000.
That included re-sealing the alfresco which was 14square metres.
If I chose not to re-seal the colours wouldn't match, I had someone who would do the concreting for $1500 but wasn't going to match the alfresco area, so I'd have 2 different colour's of concrete.
Note that I did the excavation myself and they just tidied up.
The new section is 14.35*0.9m + 14*0.9 or similar so about 25m and closer to $2800.
The concreter is charging more for this because he has to have someone with a wheelbarrow because it's down the blind side of the house and across the back, I did the digging myself but a section of the slab needs to be jackhammered to make it smooth again as its sticking out.
Also he's charging for a small drain to go below the hot water service run off, this will be connected to the plastic pipe below the gutter (a short distance from there).
So yes its expensive, you can get as low as $70 square metre, but be careful with quality. Everytime it rains the alfesco floods, the section next to it drains off into a drain, no problems on that side
Also note that this is coloured concrete (through the mix) and a sealer on top of that, not plain concrete with a sealer on top.