Pricing for SFTP Gateway version 3 on the Google marketplace is pay-as-you-go, which is $0.06 USD per hour that the VM runs. This is a software charge on top of the cost of the VM, which depends on the VM class.
To stop getting charged for SFTP Gateway, just stop (de-allocate) the VM in the Google console.
Pay as you go Pricing
SFTP Gateway uses pay-as-you-go pricing. This means that you are charged a
flat rate of $0.06 per hour for the software when you are running the VM. This pricing
applies to the software only -- there is a separate hourly cost for the underlying VM.
The VM price depends on the series and machine type (e.g.
Note: The flat rate of $0.06 applies, regardless of which VM class you choose.
The cheapest instance that the SFTP Gateway can run on is a
charges $12.23 per month for that VM.
How to stop being charged
When you want to stop getting charged for the product, you stop (deallocate) the VM in the Google Console. Deallocating will help ensure that you are no longer being metered for the underlying VM infrastructure.