Assuming cost of $1.25 per MWh (same as in California) this costs roughly $150 million. You would need 260 of these to cover all Australian households for $39 billion.
This is dayscale storage and emergency supply to stabilize electricity grid. It provides emergency supply for 30,000 homes and grid stabilization. Lithium energy competes in this category with Flywheel energy storage systems. 129 MWh's battery used alone could supply the daily electricity for something like 7000 household daily electricity usage. If it supplies only 1/4 of the electricity then 30,000 homes is realistic.
If Tesla learns how to reuse lithium with reasonable cost, this can scale. Currently Tesla recycles lithium into bricks used in construction.
The price would be $4900 per per household.
sources:
1. http://shrinkthatfootprint.com/average-household-electricity...
2. https://www.gizmodo.com.au/2017/07/all-the-details-on-teslas...
EDIT: I used average household energy usage and number of homes but used Australian population. The cost and number of units required was 3X too high. 1̶2̶0̶