It does depend if it's a power amp or just a CDP. There are transformers around which do the job perfectly. Make sure they measure more than the amp will need in wattage!
Most electronic equipment is designed for the global economy, and uses transformers that have split primary windings that can be connected either in series (for 220 v) or parallel (for 110v). Many units have a switch that the user can throw to make the changeover. If there is no switch, the rewiring job in minimal.
If the unit has a switch, the cost is zero.
If there is a jumper plug, perhaps internal, cost is trivial. Pop the cover and take a look.
If the transformer has split primary winding (almost all equipment does) the (fair) cost is 1/2 hour of labor.
If the transformer is not split winding, get a different piece of equipment.