The short answer, not very much.
A conservative estimate is that it will take at least ten years for an olive grove to break even, perhaps longer. We really don't know as there are few olive trees in the Hunter that are ten years old, and as yet no one has trees big enough to be able to reliably predict the annual yield.
Yields
At around ten years of age an olive tree should stand 3m tall and spread around 2m out from the trunk. This size tree can be expected to yield at least 40kg of fruit per year (bearing in mind that olive trees have a biennial bearing pattern).
To pick a tree using contract labour, should cost about 50c per kilo of fruit picked.
Oil olives sell for about $1 a kilo (based on 16% yield), so 40kg of olives giving 16% oil will return around $20 per tree, picked. Prices are based on the Hunter Olive Co-operative price for 2001.
Table olives sell for more ($3kg or higher), but finding a buyer could be more expensive, so return may not be much better.
How to make money out of olives.
The money is made in selling the finished product; oil, tapanade or picked fruit, not the raw ingredients. A 250ml bottle of Extra Virgin Olive Oil can sell for around $8 wholesale, about $15 retail. This contains less than 2 kilos of fruit. The grower can expect to receive $2, and spend $1 of that in harvesting costs.