Actually (june 2007) lot of banks in UB and the aimag capitals Hovd, Bayan Olgii and Uliastai change Dollar, Euro and most common to Tugrik currency. Also you can withdraw local money using a Visa card. In UB lot of banks have a 24 hour service.
ATM machines are unknown outside of UB.
Be sur you change Money befor heading to countyside, In Ulan Bataar you can change any currency, Mainly, Euros,Chinese Yuans, Russian Rubles, Swiss Francs and Dollars.
Credit card are accepted in bank counters at Hovd and Bayan Olgii, but nowhere else. Pay always in local currency and in cash
Dorm bed in a guesthouse: ca 4 dollar