Adding a shopping cart for non profits is easy to do with Volusion, unfortunately they will charge you some set-up costs. The software package is very easy to build and and maintain. You will need to set up a few other things like anti fraud and online banking. You will need a non profit account for merchant banking established.  They have a number of templates to choose fro for free and they are an established shopping cart supplier in Australia.

Drop me a line if you want more information on setting up your non profit company in Australia.