Auditor costs

ISO auditors hourly rate varies significantly from country to country, and depending on the certification body they work for, so there is no definitive answer to this question.

In this IRCA survey, you can find that global average salary for an auditor is £38,031: https://www.quality.org/knowledge/salary-survey-reveals-how-much-more-irca-auditors-earn

But please note that audit costs involves other variables, such as costs with travels and certification bodies fees. 

In case you need more precision, you can get easily require a quote from a couple of certification bodies.

This material will provide you further explanation about certification costs:
- How to Budget an ISO 27001 Implementation Project https://info.advisera.com/27001academy/free-download/how-to-budget-an-iso-27001-implementation-project