The cost of things like water, wifi, showers, trinkets, tea, alcohol, etc. are higher in higher elevation suchas Everest Region than in the urban areas. Except in Namche Bazar, you cannot use credit cards, so you have to carry cash in hand in Nepalese Currency. You can exchange your currency at a money exchange center around Thamel Bazar. We recommend you to keep around USD 250 (in Nepalese Currency!) with you to manage your additional expenses.