Should all Macca's charge the same for the same item?

Something you mightn't know is that Perth Western Australia has the most expensive coffee in Australia and I travel a lot - I have been to the US, UK, ME, Europe, Africa and Asia in the last 5 years - I can reliably inform you that the price of coffee in Perth is it right up there with the most expensive in the world.

For example, when coffee is on special in Perth, the sign often says "Melbourne prices." I get coffee in Kent Street, Sydney and for what I currently pay $4.35 in Macca's Morley I pay just $3.50.

So what reaction should reasonable when I tried a coffee at a Macca's not more than 3 kms from my normal place, and it's coffee is cheaper... which means like my local they didn't put prices up. They charged me $4.20!

I think it sucks... and I am going to say something about it... and send an email to the price gorging owners and tell them it sucks. Will anything change?? probably not but the coffee might taste better with the rant off my chest.