The toll should be most certainly be based on the rego.
I lived in NSW for 10 years and refused to get an eTag. I didn't drive on the toll roads enough to really warrant it, but it was the 'eTag deposit' that I refused to pay.
Now, to my way of thinking; a deposit is a sum that you pay, but is to be refunded when you return the item in good condition.
Not in the NSW toll road system apparently. Back when I was looking they wanted the deposit, but when I told them I would be moving interstate within a few years, the girl at the call center couldn't tell me what the procedure was for getting the deposit re-funded.
The conversation went along the lines;
So, its not a deposit, its a fee?
No, its a non refundable deposit.
So why call it a deposit if there is no facility to re-fund the money? Am I buying the tag?
No, we retain ownership of the tag, you are just using it so we can bill you.
Needless to say I wasn't impressed.
I moved to Queensland and they don't want any $$ and give me all the tags I want for nothing. Right now I have 5 on my account.
They do have SE-QLD stitched up with toll roads though. I live west of the city, so to go north, south or to the airport you are funneled onto toll roads or have to allow at least an extra hour for the trip.