The Holden Spark has been discontinued in Australia, with the company citing low volume as the main issue. But if that doesn't deter you, it's still a solid buy at under $15,000. Dealers have plenty of stock still on showroom floors, and you can get really good prices on 2017-plate models for less than $15k, drive-away. Shop for the LT if this is the car you like most, because it has a better features list than the LS.
Probably best to steer clear of the regular Barina, which is admittedly bigger, but definitely not better. The current-generation model could find its way to the automotive graveyard this year, too.
The Mirage isn't as good as either the Barina or Spark, so unless you just want a very inexpensive car, it's not high on our recommendation list. The Yaris is lagging behind the times in terms of features, but there's a reason it's a go-to for many budget car buyers: it's a strong offering for space and comfort.
All of that said, the Kia Picanto is the budget car we'd most likely recommend, because it has a strong and long warranty and is the only one in the mix with auto emergency braking (AEB). Plus it has a reversing camera as standard (the base model Spark doesn't).