MediaMarkt is a good bet for finding power converters in Budapest. They have them in most malls (Mammut, WestEnd, Árkád, Aréna Plaza, etc.) and you can also order products for delivery online.
For example, here is a 230V/110v AC to AC adapter that allows you to plug in a 110v device with a U.S./Mexico-style plug into a European outlet.
Thank you for the question, Amir! I hope this helps.