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I was in Krakow from May to September 2007 and flew there from America. I paid in dollars for my plane flight, and I didn't make any prior hotel reservations. Once you get to Krakow, the Euro is not prevalant. I used the Polish currency, Zloty, for most of my purchases.
I wanted to search out on my own for housing when arrived in Krakow. I went to an apartment rental agency by the Krakow train/bus station. That was a mistake, so wouldn't recommend for you to look for bargains located by the train/bus station. Because of course, they may feel you're desperate to find housing, so will charge you more. I paid for that first month in May $1,000 plus in studio rental fee. For the rest of my stay, I searched outside the tourist area, and found some student housing which was furnished and cost about half the May rental fee.
Not sure if they increase restaurant costs from March to April or for the Summer. I ate most meals buying from outdoor markets or the supermarket which is cheaper. If you have a microwave or cooking facilities in your rental, that will save you money.
Good luck and have nice time in Poland.