The short answer
For a small Australian business, budget somewhere between $99 and $500 a month, plus a one-off setup fee of nothing to about $2,000. The spread is enormous because the phrase covers two completely different products.
Human answering services
A traditional service is a person in a call centre taking messages from a script. Pricing is almost always a monthly minimum plus a per call or per minute rate. That structure has a trap in it: your bill goes up on exactly the months you are busiest, which are the months you can least afford a surprise.
AI answering services
Self-serve AI platforms in Australia start around $99 a month, usually with no setup fee and a free trial. You write what it knows and maintain it yourself. Managed services, where someone builds and tunes it for you, run higher and typically carry a setup fee from around $990.
What the setup fee is actually for
Nothing to do with technology. It pays for someone to work out what your receptionist needs to know, what it must never guess at, and then test it until it holds up. A platform with no setup fee has simply moved that job to you.
The number that actually matters
Not the monthly. Work out what you are losing instead. Calls that ring out in a week, times the share that would have become work, times what that work is worth. Most trade and service businesses find the answer is several times the cost of covering the phone, which makes the monthly figure close to irrelevant.
What to check before you sign
Whether there are per minute or per call overages, whether there is a lock-in period, whether the setup is done for you or by you, and who you ring when it stops working. That last one separates the products more than the price does.