I don't live in Melbourne so didn't want to pay up front for an E-tag that I would hardly ever use.

I found instead I could open an account with Citylink (no cost to do this). So now I just drive anywhere I like and if I happen to go through any of those toll points they look up my rego and a week or two later just take it out of my credit card. The only extra charge over having an E-tag is a rego-spotters fee - about $1.50 for the day I think.

It's great - I've never had to deal with Citylink since.