99% of retails outlets have eftpos so all the Commonwealth needs to do is setup a debit style card. One of the major banks could even administer it. With so many cards it could be done very cheap. How many Medicare cards out there??
Make it illegal to buy alcohol or gambling tokens with it for example and make the retail outlets accountable. Make the card a distinctive commonwealth voucher card with the illegal contraband stated on the back. Showing your ID at the point of sale costs NOTHING.
Educate and make the retail sector and general public aware of what can be and what can't be bought with the card through advertising. Imagine how much advertising you could do with $50mil.
That way its not going to be wasted on gambling or alcohol or even illegal drugs. No money could be simply banked. No money could be taken overseas on that holiday. The money would have no choice but to go into the Australian system and stimulate the economy.
