Got these prices from German retailer Vesalia.
(
www.vesalia.de)
OS 3.1 Disks 9.90 EUR
ROM 3.1 19.90 EUR
I'm not sure about the exchange rate but guess 1.6 or 1.7. That would
give the 16 or 17 Australian dollars for the OS disks.
But for orders this small it usually doesn't pay off to order from
abroad.
You may be right that 3.5 and 3.9 requires a 020 or better to work.
And even if the OS doesn't requires it, the third party add-ons
surely does.