If you've lost the only key to your car and there's no spare anywhere, the situation goes from "call a locksmith" to a slightly bigger job. Here's what you're actually looking at.
Step 1: confirm there's no spare
Worth a serious search first. Check the obvious spots, then the unobvious ones. Old handbags. Coat pockets. The car itself (we've found spares under floor mats). Mate's place. The lockbox at your old rental. Even your dealer might have a record of a second key being supplied at purchase.
What kind of key your car has changes everything
For cars pre-2000: typically a basic mechanical key, no transponder chip. A local auto locksmith can cut a new key from the lock code on your VIN within an hour. Cost around $150-$280.
For cars 2000-2015 with a transponder: the new key needs to be programmed to your car's immobiliser. Most makes can be done by a mobile auto locksmith. Cost around $300-$600 depending on the model.
For 2015+ cars with proximity smart keys: programming is more involved. Many makes require dealer programming. Cost $500-$1,500 plus a possible tow to the dealer. Some makes like Toyota and Mazda have wider third-party support and a mobile locksmith can often do it cheaper.
What you'll need
Photo ID showing you match the registration. Proof of ownership - current rego, recent insurance certificate. The locksmith won't cut keys to a car they can't confirm is yours, for obvious reasons.
The dealer vs mobile locksmith question
Dealers are often more expensive but always reliable. They have manufacturer programming software guaranteed to work.
Mobile auto locksmiths in Bendigo are usually cheaper and can attend on-site. The risk is if your specific model isn't well-supported, you might pay for a callout that ends with 'we can't do this one, you'll need to go to the dealer.' Reputable locksmiths ask the year, make and model first and tell you upfront.
If you're really stuck
If the car is unregistered, has been off the road for years, or you can't prove ownership, you'll need to work through the dealer with proof from the registration office. Slower and more expensive but the only legitimate path. Don't try to get a key cut by misrepresenting ownership - locksmiths report it and the police are involved.