Because everything must be ‘imported,’ costs are higher than in other cities.
Several banks provide an ATM, including BCP, which has secure ATMs.
Several banks change traveler’s checks and give advances on credit cards, including BCP. For changing US cash quickly, street moneychangers are located on Próspero between Lores and Brasil. Most are OK, but exercise caution changing money on the street: it's best to do this in a bank. For the Peru/Brazil/Colombia tri-border, the border towns have money changers anyway. Transfer money at Western Union.