Regarding the costs, for an employee the cost is pretty much know, it's their salary, for AI not so much. There is the implementation cost, one time and mostly known, but even here additional costs can creep. Next are the monthly costs, depending on how stuff gets implemented, there could be maintenance and API costs, and a bunch of others(electricity, server rent, etc.). Most analyses I've seen, show that in the end AI costs the company more then the employee they replace without any real boost to performance. A recent study actually suggests that companies that give AI as a tool for their employees see an increase in performance, but most of the ones that replace employees with AI see a decrees in performance.
Fun story an admin friend told me, a company replaced on of their accountants with AI, the job was to mostly pull data from various sources and compile financial reports. Another of the accountants used these reports for IRS(well the equivalent over here) related documents. One day the AI seems to not have been able to get data from some of the sources, but instead of informing someone, it decided to just hallucinate up numbers, which ended up being submitted to the IRS and got the company a fine.