Use Blue Circle Southern Cement Easy Estimator to estimate the raw materials such as cement, sand and stone or gravel you need.

From the page, you can find out:
Suggested concrete mix designs: High Strength & Water Tight, General Use (paths, floors, etc.), Foundations & Large Masses
How much to order to fill 1 cubic metre (m³)?
Suggested mortar mix designs for bricklaying
How much concrete do I need for fence posts?

Mortar is a mixture of sand, cement, water and lime. Mortar acts as the bonding agent between bricks and blocks, as well as the medium that accommodates variations in their dimensions.

When you work out the cost of concreting, you need to consider not only the concrete poured (for example, $110 per m2), but also reo bars because they are not cheap.