Which ITIL process is responsible for creating the cost agreements for extra support of the Service Desk?

The Service Level Management (SLM) process is responsible for creating the cost agreements for extra support of the Service Desk. The purpose of SLM is to negotiate Service Level Agreements (SLA) and Operational Level Agreements (OLA) with customers, in order to design services that are mutually beneficial for both parties involved.

Another component of SLM is to monitor and report on the current status and level of service in an ongoing way. The five stages in the ITIL V3 Service Lifecycle are Service Strategy, Service Design, Service Transition, Service Operation, and Continual Service Improvement.