ISO 27001 budgeting

Broadly speaking, I can suggest these main topics to consider:

OPEX:

• Training and literature
• External assistance
• The certification process

CAPEX:

• Technologies to be updated/implemented

Regarding ISMS maintenance costs, the above-mentioned costs also have to be considered, but at different levels, and you have to add the surveillance audit costs for certification maintenance.

These articles can provide you more information:

• How much does ISO 27001 implementation cost? https://advisera.com/27001academy/blog/2011/02/08/how-much-does-iso-27001-implementation-cost/
• 5 ways to avoid overhead with ISO 27001 (and keep the costs down) https://advisera.com/27001academy/blog/2012/06/19/5-ways-to-avoid-overhead-with-iso-27001-and-keep-the-costs-down/
• How to Budget an ISO 27001 Implementation Project https://info.advisera.com/27001academy/free-download/how-to-budget-an-iso-27001-implementation-project