score:1
if you want live on a budget, you need to exchange cash - small shops don't take Euros or Credit Cards, or only on horrible rates.
If you go in middle class restaurants, you probably can pay with credit cards (no Euros).
Generally, those countries have lower cost of living; but as you will be in 'Tourist Central', you will easily pay equal or more than in western Europe.
Upvote:0
My advice would be to choose a bank in your home country that has low or no conversion fees, and primarily use an account in your income currency. I travelled to all three cities, and have rarely ran into cash-only places.
Since you're saying you're only there for less than 2 days,
For Prague, you can learn a lot from the Honest Guide Prague YouTube channel. For example, their take on budget restaurants from 2016 still holds.
Upvote:2
Our usual advice, and it holds for Hungary and the Czech Republic, is to find an ATM card with no foreign transaction charge, and use it as much as possible. Every tourist-oriented concern I went to in Prague and Budapest took plastic. Indeed, American Express was running a special promotion with the cinema for 15% off: usually that's a lousy card to use overseas.
If you can't find such a card, I would attempt to pay with Euros, which will be accepted at some exchange rate, likely poor. However, neither the koruna nor forint will be easy to exchange outside their home country, and I think you will lose even more bringing your change from 100€ home.