Forwarding rules and processed data.
A Google Cloud load balancer bills in two parts: an hourly charge for each forwarding rule whether or not anything uses it, and a per-gigabyte charge for data it processes. The hourly part is why a forgotten test load balancer costs money for months.
Billed: An hourly charge per forwarding rule (first five priced together, then per rule) plus a per-gibibyte data-processing charge.