Most establishments (certainly fixed wing) have a standard basic rate for scheduled servicing. In our world: 50hr, 150hr, Annual and Star Annual.
The cost quoted is for the inspections in accordance with the CAA Light Aircraft Maintenance Schedule (which exists for rotary stuff as well as fixed wing) CAP 411.
Any defect rectification, parts and labour for said defect rectification are charged on top of that. Pretty much as car servicing is done normally.