How much does it cost to replace the back of an iPhone 4 in Australia?

I shattered the back of my iPhone 4 today, and it's leaving little cuts on my fingers from holding it, I'm wondering how much it will cost to get it replaced/repaired in Australia (Queensland). I've heard sometimes it's free, sometimes it's $29, and that it could cost me $200!!

Also how much I would have to pay for them to just replace it with a 5, thanks 🙂

(I do not have any warranty or insurance...)