Hiya im in aus too and I know 2
Jai's both are exactly as you put it 'white Australians in their 20s' :)
I pronounce it like
Kai, with a long ee sound after the ja, plus an australian accent.
As far as i can tell its not related to
Jay, id group jay in more with the
Jayden realm.
Not really a fan of
Jai or
Jay.
https://www.behindthename.com/pnl/145466