What is a good European to US voltage converter?

I recently purchased a guitar combo set from a website the website www.thomann.de as a gift. After purchasing the set, I was told that the amplifier would not be able to be sent to me because these amplifiers run on a different voltage current. I was informed the voltage is 230 V and 50 Hz. I was told that in order... show more I recently purchased a guitar combo set from a website the website www.thomann.de as a gift. After purchasing the set, I was told that the amplifier would not be able to be sent to me because these amplifiers run on a different voltage current. I was informed the voltage is 230 V and 50 Hz. I was told that in order to run the amp in the US, I would need a "voltage transformer".

My question is, what is a suitable, inexpensive voltage adapter that I can purchase that would allow me to run this amplifier. Thank you.
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