It’s difficult to give an exact amount of money that you should bring. Costs will vary according to how much time you spend traveling on your own, whether or not you go trekking/traveling, if you drink beer (!), how often you phone home / use the internet etc.
That said, living in the village is very cheap as you will not have to pay for your main food or accommodation and there is very little for you to spend your money on! During your training and placement you are responsible for any incidentals (sodas, snacks, etc.) that you may accrue. We recommend purchasing one of the travel guides, such as the Lonely Planet for Nepal to help you estimate how much money you may need. Don’t forget that you also need to budget for program fees, visa fees and your flight and any extra activities, extra transportation and extra food.