Buying common property (front garden)

Hi flat chatters, looking for some advice if possible, please. 

We live in a unit, in what is not Sydney’s most attractive street, in Hillsdale. We are on the ground floor and are toying with the idea of trying to purchase some of the common property at the front of the building, i.e. part of the front garden outside our unit, so we can install a door from our kitchen opening to the area, which we would fence and turn into an alfresco patio. 

I think we’d go down the special resolution path and try to get approval from 75% of the OC and transfer the purchase cost to the scheme’s trust fund. There’s a good chance we would get it approved – we are lucky in that sense – however, I wondered whether anyone could give me an idea of the going rate of this sort of area? 

We’d of course hire an independant valuer if we were to go ahead with it, but I have no clue as to even the ball park! The area is approx 2mx8m (16m2). 

TIA for any help offered.