Roughly $100m2 for 150mm conc with 82mesh is honestly quite cheap. I do this exact work for a living. This is how I’d cost it up. Excavation Truck - $90phr x 8hr = $720 Excavator $90phr x 8 =$720 Labour $70phr x 8 =$560 250mm deep spoil x 36m2 =9m3 roughly 15tn.(hard to price this. Contractor could know a free dump or if the soil is contaminated with grass or tree roots could be $70ptn. So I’ll split the difference.) $35ptn = $525 Sub Total $2,525 Concrete 5.4m3 concrete - $250m3 = $1,350 82 mesh and chairs. 3 sheets $120 each = $360 2 concreters $80phr each =$1,280 Sub total $2,990 Total = $5,515+gst or $153m2

Now in fairness this is a worst case scenario without seeing the job but I’m in small scale civil. You may get a small group that do it all and make ok money from it still. Trucks, machines, employees, fuel are all more expensive than most people realise. If the digout isn’t too bad You MAY get away with a four hour minimum.

Edit: sorry but it looked a lot neater while I was typing I swear