The first month is not the ongoing cost
Almost every account needs work before management even means anything: conversion tracking that reports the right events, a structure that separates what should be separated, and a baseline recorded so later claims have something to be measured against.
Budget for that as a project, separately from the ongoing management fee. Rolling it into month one of a retainer is how a retainer starts looking expensive.
- Tracking and attribution audit, then fixes
- Account structure and campaign rebuild
- Baseline recorded before any change ships
- Creative and landing-page testing plan