It is better to obtain Hungarian Forints upon arrival to Hungary than to exchange it with a bank at home, as local Hungarian banks work with better rates than their counterparts abroad. Exchanging foreign currency into Forints is therefore possible in banks, official currency exchange offices (these are affiliates of larger banks) and travel agencies.
It is important to know that all official currency exchange offices determine the exchange rate on their own accord.
They must fully inform you about their own rates, but not the real or the best exchange rate available - they build their costs into their very own rate.
The exchange rates must be visibly displayed at the place of exchange. Changing money at Budapest hotels is not advisable, as their rates are at least 10% lower than what is generally available.
Under no circumstances you should change money illegally in the street: beside the possible legal consequences, it is highly probable that you will be cheated in one of the hundred possible ways the street criminals can devise.
Most international credit cards are accepted in Budapest for shopping and currency withdrawals:
AmEX Diners Club Maestro EnRoute Euro/MasterCard JCB Visa