For NSW Residents Only
Promotion is called a Sydneysider Pass.
If you pay for a 7 day flexiticket in March for yourself, and bring in NSW ID, you can have unlimited visits to Sydney Tower for the balance of the year.
Adult cost for flexiticket is $25 and child is $15
See the link for further details. Entry is just to the observation level, not the Skywalk, which costs extra.
A good deal if you make sure to repeat visit - you could start a tour guide business with this deal :)