4TB in single drive. Of course, you can get multiple bay enclosure and put more in there. For consumer, usually 2 to 8 bay so giving you 8 to 32TB.
You can find them in your local computer hardware store or on internet hardware store.
In Australia:
www.staticice.com.au
search for the terms and it gives you the price of major computer shops in Australia
In USA and Canada:
www.newegg.com
www.newegg.ca