Wilston Vet is having a special on microchipping on 20/3 between 9-1pm. Usually $79, at this time will be $25. Bookings required.
I'm not affiliated with them in any way and don't have any further info, just went past and saw the sign and thought it might be helpful for someone.
It's not mentioned on the website, I gather you just mention it when you call to book.
(Edit - corrected date in title)