30 calendar days. ~80 working hours. The deliverable is one functional spec the customer signs. Most consultancies spend that budget on workshops; I spend it on writing.
Day 1–3: read whatever the customer already has. Spreadsheets, screenshots of their current ERP, the email thread where they wrote out the plan in 200 words. Don't have a workshop yet — it'll be useless until you can frame the right questions.
Day 4–10: one workshop, one stakeholder, one process at a time. Three workshops max in week one. After each: write the section of the spec covering that process, send it back the same day. The customer's correction is more valuable than their original explanation.
Day 11–25: keep writing. Quote a price for each module, conservatively. Push back when scope creeps — the goal is a signable doc, not a complete one.
Day 26–30: review with the customer, finalise pricing, get the signature. If you've been doing it right, the doc is already what they expected.