Not sure if this helps and i am by no means an expert but my mum applied in aug 2016 for her 143 and the plan was to come out for 6 months over christmas. She applied for the 600 tourist visa just as shes done many times before and was asked by immi if she wanted to go for the new 5 year parent visa which she has. So the rules are 12 months stay in any 18 months, she had to take out private medical approx $200 pm for basic cover and its valid for 5 year's so she can come and go within the rules until 2021. She cannot apply for another visa - this doesnt affect her existing 143 application though. Cost was same as 12m e600 visa - one off cost. Hope that makes sense - she has to go home for at least 6m after being here for 12m.
Leigh-anne