You can withdraw with your debit cards also at the ATM's.
You should be able to get some money ex-changed from the banks on the friday though either morning at 9.00 or after skiing but they do close around 4.30 usually.
There is one up top end of town near you up past Kempinski.
Exchange rate in UK was 2.08 to £ exchanged £20 in the local bank and got exchange rate of 2.28 to the £. Do not use local little money stands only use a bank and its well worth the effort.
Alpha bank near to the square had started to open Saturday mornings through the season, to cope with the deluge of punters we had recommended to go there hehehehe deffo the best rate in town, and the friendliest manager Nikolay... tell him Steve sent you