hey, well here are some info which i think will help. the average cost depends on the kind of life style you choose to have. to lead an average but really confortable life, for example a monthly grocery items for a family of 4 purchased from high class marts will be like around $250-350.
if you prefer to dine out, the cost will be slightly higher than that amount but not too higher. again depends on the kind of place you want to dine.
live-in made, a nanny will not cost you more than $50 per month. a made that do the cleaning and cooking, well nowadays there are trained maids and they cost from $70-100. def not more than that. an average home(3-4 bedrooms) again located in nice and ´safe´ residential area will cost you not more than $1000/month. i quoted safe coz the country in general is very safe. at least that is something we Ethiopians are proud of. utility costs icluding cable TV will not exceed $200-300/month. there are so many newly established residential areas to choose from. at least the once i know are Jakross, Ayat, CMC and Bole areas where ppl with higher standards of life live. and you can find an average home by the cost i mentioned in this areas. when it comes to schools, there are international and quality schools.
in general, i am sure you will find Addis totally different from the one you have in mind. i mean there are places that makes you forgot you are in ´Ethiopia´ and places that remind u where you are. but over all no doubt you will enjoy it i hope this helped....slight change of costs might be there since i left Addis last Yr and since you are planning to move next year but i tried to consider that also.