電費: 用冷氣的風扇貴，還是用普通風扇

You are right that the compressor is not used.

However, the motor for spinning is larger than that of an electric fan. Mostly importantly, you don't get direct wind blow from the air-con unless you stand right in front of it.

Therefore, it's more economical to use electric fan instead of the fan function of air-con.