This is a question that gets brought up a lot with my job on a daily basis. If you base your math off a standard 52inch 4 blade ceiling fan with fan settings built into it as slow, medium and fast. Let’s say we were running this fan at medium speed the average hourly running cost for the fan would be roughly 0.28c. If you were to have that fan running at 4 hours a day for 365 days a year the annual running costs would be $4.40 roughly (depending on electricity usage rate as well). If you have multiple ceiling fans running or fans were left on when no one is using it the costs would creep up on you.
If you were to have air-conditioning the average reverse cycle split system costs roughly between $0.33 and $0.45 per hour. This is unquestionably more expensive to run then even a stronger and more powerful ceiling fan. An air conditioner is more effective at cooling rooms or even heating rooms, but you are definitely paying for it when it comes to the usage.
Evidentially you could save hundreds on your annual electricity costs if you ran fans at low to moderate speeds throughout the day rather than the air conditioner.