To design a GCP solution that meets Google's best practices for operating nationally with multiple batch workloads, including some that are not time-critical, and using HIPAA-compliant services while managing service costs, you should provision standard VMs in the same region to reduce cost, and use GCP services that are HIPAA-compliant as needed. Therefore, the correct option is C.
Preemptible VMs can provide cost savings, but they are not recommended for workloads that are not time-critical, as they may be interrupted at any time. Provisioning standard VMs in the same region will provide better performance and stability, and can still be cost-effective by using features such as sustained-use discounts and committed use discounts.