Found this offer on Jetstar website. Club Jetstar members will now get exclusive access to $1 fare sales (8 passengers per booking) up to 4 times a year and other discounts. It does cost $39.95 to join Club Jetstar though but it will be still be worth joining if you travel with family at-least once a year.
I am copying the full details below from Jetstar website.
Club Jetstar is a new membership program from Jetstar. For a once-off AUD$39 joining fee, and a low ongoing annual membership fee after the first year, it provides members with:
• Exclusive access to at least 4 member only Club Jetstar sale events, including $1 sale fares, each year
• Discounts and special offers from a range of our partners
• In addition to the joining fee, an annual membership fee of $39.99 applies after the first 12 months
• Both the joining fee and the annual membership fee are not refundable