There's no charge if the issue is covered under warranty, AppleCare+, or consumer law. If your issue isn't covered, you'll pay an out-of-warranty service fee.
The HomePod, which was released today, costs $349. If you require shipping for your HomePod repair that's an additional $19.95 fee and it brings the total to $298.95, nearly the cost of a new device.
You can learn more about HomePod service options, warranty, and pricing at the link below.