If a decision can be written down as a short rule, the rule will be cheaper, faster and more predictable than a model. Calculating a cost from a table does not need AI.
AI is useful where there is free text, voice or images and where the result can be checked.
If the cost of an error is high and nobody can check the result, a model should not be used without human control.
Often the best option is mixed: rules handle the exact part, and a model parses the unstructured data.