It's hard to say right off, without knowing the I's circumstances.
Do you have anyone to stay with, or are you relying on hotels?
Are you traveling a lot or staying in one place?
What level of comfort are you comfortable with?
it would be a lot easier to say if I knew , but for myself, when I'm not staying with family or friends
In Addis hotels with a hot shower and a decent room can run from 6 or 7 dollars a night or nicer places can be like 30 a night, however there's lots of simpler places, but fine in my own sights, that run about 3 dollars a night, and there still may be a cold shower in the room if not a shared one outside. Outside of Addis hotels get even better value for the money. Food is cheap, that will probably be the last of the I's concerns. One thing I found though was that learning to count in Amharic was extremely helpful in getting the right price. I've found that I got around real well on 100 dollars a week, but it could easily be done for less.