Software Estimation

For those developing SaaS web applications, could you share your experiences with receiving detailed cost estimates from software development agencies based on your SRS documents? Specifically, I'm interested in whether these estimates include a breakdown of the time required for front-end and back-end coding for each Figma screen, and if they apply the standard 160-hour work month (40 hours per week for 4 weeks) for each team member (front-end, back-end, DevOps, QA Engineer, Project Manager, Tech Lead).