Personally, I wouldn't bother with a second hand stereo...Considering some of these stereos will be up to 15 years old now
If you're not into the whole doof doof nightclub on wheels audio setup, you can buy a good quality stereo from Supercheap Auto with Bluetooth & USB for around $100 when they have sales on.
Holmarts prices are ridiculous, most of their stock has increased or in some cases doubled in price.......and it seems to have occurred since Holden ceased manufacturing.
For about $100-$150 more than what Holmart are asking you can get a new plug and play double din unit with, Sat Nav, Bluetooth & USB, internet connection capabilities, internal memory space to store up to 20 CD's, reversing camera and a whole host of other gadgetry that can be added onto it.