Prices are fairly close between Astro suppliers in Oz in a small competitive market , they do vary but not by much 1 to 5% ( unless they have a stock clearance sale etc... )
Avoid using retailers !!! Eg: National Geographic shops
Bintel is a popular supplier , so is Andrews Communications
Both are located in Sydney and both have great service and support
You can buy Direct from overseas websites too but it can be troublesome with no local support.
I have purchased from both over the past 5 years with no issues
https://www.bintel.com.au/
There’s a few in Brisbane and Melbourne too
Hope the above helps