people have begun doing them to Cambodia, Malaysia and Vietnam as restrictions drop and with land borders opening Laos will also be a possibility (maybe avoid Myanmar). However, if you're not bothered about actually visiting those places then have a look to see if the STV visa is still a thing. It was introduced for covid, then they were going to scrap it and then they reintroduced it. I've not looked recently to see if it's still a thing Cost will be about $120 Australian. You'll have to show proof of funds for your length of stay and they'll ask to see accomodation booking for the time there but a cancelable booking on Agoda or booking.com should be enough to satisfy them)
The only proviso to that is the possibility of covid extensions being allowed still but with land borders now opening it seems very unlikely that they will extend those past this month
If they're still offering the STV that can give you up to 9 months. Otherwise you'll be looking at a border bounce as regular tourist visa (60 days) and visa exempt (30 days) both only allow 1 extension of 30 days
Return tickets tend to be cheaper than one way anyway so you might be better off getting that. Even if it's a non refundable you should still get your taxes back if you cancel the return leg