Payment methods? How long has it been out of Rego for?
Typically, if it does run out of rego, you will need to get the car roadworthied to re-register it.
As far as the payment for the rego goes, you dont have many options.
They require an annual payment of the rego fee to be paid in full.
If you have a health care card, you can pay half every six months, which makes it a bit easier.
I would definately get in touch with VicRoads asap. If it has only just expired, you might be able to get away with paying the rego fee without getting a RWC, otherwise, you are probably up for alot of other fees to re-register your car.