Hardware and software, SaaS licensing, cloud costs, etc.
Hiring costs (recruitment, recruiters, time lost in selection and hiring)
Secondary cost to rest of the business to change processes, retrain, integrate, help the dev team understand requirements, effectively build and iterate, etc.
Quite possibly a bunch of compliance, security, audit, pen testing, and other regulatory costs depending on the demands their clients have, etc.
Running a team != hiring a bunch of freelancers as a one-off.
Stop giving the guy horrible advice. IF you think throwing some freelance devs with no business support/product/UX support is going to help him, you are so mistaken. Trying to rebuild an existing complex software system that handles hundreds of millions in revenue is not going to be an easy task. You are going to put the man into a corner and ruin him. Jesus.
Office space
Hardware and software, SaaS licensing, cloud costs, etc.
Hiring costs (recruitment, recruiters, time lost in selection and hiring)
Secondary cost to rest of the business to change processes, retrain, integrate, help the dev team understand requirements, effectively build and iterate, etc.
Quite possibly a bunch of compliance, security, audit, pen testing, and other regulatory costs depending on the demands their clients have, etc.
Running a team != hiring a bunch of freelancers as a one-off.