Countries like Hungary or Poland are now better in accepting credit/debit cards than many countries in Western Europe. We spent 4 days in in BUD last year and paid for everything with credit cards: bus from/to BUD, subway, meals in the restaurants, water and small snacks at local grocery stores, stuff at Starbucks etc. No need to have Forints.

PS. We have never used taxis as subway system is very efficient and stayed at Interconti that is within the walking distance to the airport bus stop (we traveled HBO).