Laptop Batteries Australia - Acer Aspire S3

I bought the Acer Aspire S3-391 off of another student on Gumtree.
I managed to get it quite cheap because the battery had degraded, and I wasn't intending on using it away from a power outlet, but no I've had it for a few months, I've realised how much I need a working battery.

So my question is where can I find a battery that isn't going to cost over $100.
Or does anyone know how I could construct my own with a few flat Li-ion cells.



I have an Acer aspire E1 531 you can have for cheap - hell for $100 I'll express post it to you with tracking anywhere in Aus (or pickup from ACT if you're local)