There are a lots of places where you are able to pay in Euros, but it is not the best option. There is no know exception: They do not offer a correct exchange rate for you by Euro payment. You would do it better to change your currency in advance at any of the licenced Exchange Buroes (be careful, there are extremly bad rates at several places) or in a Bank. Banks are also not an economic option for money exchange. But at least you get more Forints (HUF) for your money than for example in a restaurant which accepts your Euro. It is adwisable NOT to change your money at strangers on the streets. They are scamming at most of the times.