taxi fare would be high. i suggest renting a car with driver is a better option. for reasonable rate pls visit mekina.net or call 0911235133, 0921752807 low profiled car rental services near stadium.
monthly fee preferable. let the driver collect his salary from the renter and you keep the car overnight, if not keep registering mileage.
but if you dnt need the service of the vehicle full day, that means if it is only two ways trip, it is better to get lada/Corolla taxi.
Gabriel church/lafto mall-Addis Ababa Univ.- Gabriel church/lafto mall would be not more than 200 birr. two ways of course.
hope this helps.
Liz