Using CryptoCurrencies as a transfer method throughout Australia and Europe
The most "profitable" way i can think of doing this is:

1) Your cousin buy BTC with AUD in Australia in some local exchange (preferrable) or at LocalBitcoins.com

2) You sell the BTC in Europe using LocalBitcoins (your cousin will give you the password for his LBC account or transfer the BTCs to your account there). They have a 1% fee for sellers, but you could just advertise with a 1% profit, or even more, because prices in LBC are usually higher than at local exchanges. In my country i can easily sell with up to 3% profit.


No expensive international bank fees
You receive the money directly in your bank account


I don't know if using Stable coins would be a good idea, as you'd probably have to pay some convertion fee to redeem them in Europe.

Anyways, it will mostly depend on the volume you're dealing with and the time you've available.

For example, i don't think it will be easy to sell ~300 BTC in LocalBitcoins.

I think the most sensitive part is selling the coins (it's the part the fees are usually higher). If you're dealing with higher volumes you should probably look for a local OTC desk (exchanges have that and the fees are negotiable).