Google's KMS pricing structure is $0.06/key/month + $0.03/10,000 encrypts/decrypts [0].
At $0.06/key/month, that's practically free for most reasonable use cases. For example, if there's 10k secrets that's $7,200/year.
If you encrypt/decrypt your secrets 1 million times per day (~11.6 times/s), the access charges would be $1,095/year (1 million operations/day * 365 days/year * $0.03 / 10,000 operations).
At $0.06/key/month, that's practically free for most reasonable use cases. For example, if there's 10k secrets that's $7,200/year.
If you encrypt/decrypt your secrets 1 million times per day (~11.6 times/s), the access charges would be $1,095/year (1 million operations/day * 365 days/year * $0.03 / 10,000 operations).
[0]: https://cloud.google.com/kms