I moved from US to Spain early last year and brought most of my gear with me. I did not get a voltage transformer.
I dumped my voodoo supplies as they are fixed at 110 volts input. Picked up a TRex for my smaller board and Cioks for the larger as they have selectable input voltage 110-220 volt. As a backup, I also brought my 1Spot and Godlyke Powerall, which are suitable for 110-220 volt, only need an adapter plug so that it can be used in the European socket. The adapter plug is much more convenient than a voltage transformer.
For most DC powered gear, including guitar effects, computers, cell phones, etc., voltage transformers are not really necessary as the power adapters are generally capable of supporting input voltage 100-240 volts. 50/60 Hz is generally not an issue. Only thing necessary is the correct plug end.
If you can get away with a 1spot or similar switcmode supply, this would be the best most cost effective external power supply option.
Of course, the easiest solution would be battery power, but that may not be an option for you...