The first bit of content will concern the construction of the site itself, which can be viewed in the Makefile.
I also deploy my site for music to GCP, though that is currently using Hugo pushing to Cloud Storage. When I initially set it up I configured it for global access, but have since realized that costs me a small amount monthly... at the moment I'm not expecting the site to be covering any expenses and I'm not delusional enough to expect to need global coverage so I've gone back to reconfigure it to reduce such costs. It's certainly still not costly, but I'd expect these sites to typically fit comfortably within free'ish tiers.
After the costs have continued it certainly appears as though the readily supported combination of load balancers and object storage preclude free tier use, so I'll likely adjust the site to use Cloud Run similar to this one.
Replacing the load balancer with a regional configuration would hopefully reduce the costs (I did knock the site offline for a brief period but continuing from the above this was unlikely to have any consequence for this site) but as of right now I'm still getting dinged for some lingering resources. I tracked down a static IP that needed to be removed, and there were also some lingering forwarding rules. I'll have to check the billing (or just wait a month to see if I'm still getting charged).