What will doing this ourselves cost?

Internal time, professional review and implementation still have costs. No universal DIY budget is defensible from the evidence retrieved. Use your staff’s loaded hourly costs and actual supplier quotes; the publicly advertised Cerebral design range is a single-supplier example, not a ceiling or industry norm. Cerebral Tax Advisors — Pricing and scope

Common failure points are incomplete books, signing before the incumbent reviews the assumptions, treating a tax refund as proof of incremental value and missing a specialist’s lead time. The cheapest useful first action is often the baseline meeting.