I need to protect it with 'intellectual property' laws? Does anyone have any ideas how much this costs to do at all?
I have a program that I've developed
It depends on what the program does and how it impacts your clients.
You can look at www.ipaustralia.gov.au for basic information about copyright. However you'll need to speak with a lawyer who specifically works in the field of technology and ask them to prepare terms and conditions of use or an end user licence for you. That would be an agreement between yourself and your clients about the use of the program. You'll also need to consider appropriate insurance for your business as many off the shelf insurance products wouldn't necessarily be designed for technology businesses.