Change shaded pole motor to another?

What do the manufacturers' price lists say?

Cost of motor probably exceeds the power difference you will use. At 10 to 30 watts you have less power than most light bulbs.

Other factors to consider is if motor runs in a stall condition, very common for many actuator motors for furnace valves.

Synchronous motors need asynchronous starter (circuit or additional shaded-pole part) so you cannot win anything.

Usually shaded pole motors are used in very low HP applications like condensor or evaporator fan motors for domestic refrigerators/freezers. I don't think there would be much savings benefit from replacing such a motor.