God
Hey!
I have friends that go to both of the colleges mentioned and they both have said Newman and St Hildas are pretty good!
If Newman is cheaper (like you mentioned, $6K), I would definitely be taking that option. Newman has a really good culture based on what I've heard and I tend to hear a lot going on in comparison to St Hilda's. Newman I would say is the most religious college but I know plenty of people who are not religious but are in the college, you will be fine either way. I don't know as many people from St Hilda's as I do at Newman, but it seems to be a more chill college and a little smaller (which you may like!). No matter which option you pick, it will be good!
TLDR: Personally would take Newman over St Hilda's not only for financial reasons but the culture of the college is good. Hope that helps!