A full range of Cycling computers is on sale at 99 Bikes. Prices range from $26 to $900. You get what you pay for. Navigation with maps starts around $400. Colour screens with maps are better than black and white screens.
While this article refers to the 99 Bikes sale, Pushys had a better deal on the Garmin Edge 530 GPS Bike Computer that was discounted to $399 on 20/7/2020 ($100 off RRP). It is always worth checking the larger retailers in Canberra as they are competitive.