Bank cards (credit or debit cards) widely accepted in shops and restaurants and even in some bars too. This is the most convenient and cheapest way of paying in Budapest. Of course there are places when you will need cash.
Euro – sometimes Dollars and Sterling too – are widely accepted in the shops restaurants or even bars in the city centre but it is not a good idea to pay with them since these places use very bed exchange rates
It is better to change money in many of the legit change offices you can find in and around the city centre. Just check the daily rates on the internet and chose an exchange kiosk which offer a rate close to this. They charge 0.3% mandatory commission. Just be sure that you don’t change at the railway stations and at the airport – there work with terrible rates.
Always avoid changing your money on the street, as you will most likely be scammed.
ATM machines are also plenty and easy to use. Best to use an ATM with a bank office behind instead stand alone machine on the street and shop windows since they tend to work with a worse rate and fees than bank ATMs.
If you plan on travelling to the countryside, be sure to take some cash with you as there are only few places accept bank cards – but you can still find some ATMs.