Australian Tech

If they've got other internet access, the cheap annual plans with like catchmobile and kogan are probably the most frugal for a local number. Else they can cycle through into month pre-paid offers. $5-10 a month then ditch the plan, be sure to turn off auto renew. Probably want to make sure the handset works in Australia given we blocked a bunch of models recently.

https://www.amaysim.com.au/sim-plans/28-day-sim-plans/unlimited-small

This is cheap as chips and you can get a physical sim. $10 for 10gb and 28 days of usage. $22 for another month of use after that.

PS. I bought a large hot chips for $10 today.

If they are just staying in cities, Vodafone seems to have good offers for travellers. However one of the mvna operators would be better for a better network of outside cities too.

Look at sim only plans that are month to month.

Pay-as-you go as in "I pay once a month for everything" or "I pay a minimum set fee and then all calls + data on top"?

Many of the cheap plans are only available as 365-day prepaid, which might not suit your friend. I use a Catchconnect 365-day plan that was super-discounted around new financial year last year (I think it was $85ish/year including all calls and some data on top, which is enough for me).

Some time last year all Optus MVNOs increased their prices. Moosmobile used to be $8/month, now it's 15/month.

http://wizard.id.au/spreadsheet/australian-mobile-cap-plan-comparison/

Whirlpool forums are a great place for Aussie telco information.