Use the GCP Cloud DNS Service Instead
An organization with 1 managed DNS zone and 1,000,000 queries per month would only accrue $0.60 of billing per month. Meanwhile, an unused reserved IP address costs $7.20 (per reserved address) per month. Used address reservations cost slightly less at $2.88 (per reserved address) per month. So, an organization can be charged per static IP address, or use a managed zone that supports millions of records.
More on Google Network pricing here: https://cloud.google.com/vpc/network-pricing
If there is a managed DNS zone, then a record can be assigned to the VM within the Compute Engine. From this point, API calls can be used to update the DNS records as needed. In this way, hostnames are used to reference a system with a dynamic public IP address without the need to manually update the change the IP address each time. This is accomplished by setting a start-up script on the VM. It will download the DNS update script, and then set it to run each time the host reboots.
Cloud DNS is a very cost effective service. Many companies would prefer to leverage this solution over static IP addresses, which is more costly. An environment that leverages this solution would operate like this: