There has been no sign of a feasibility study or figures from government officials on ethiopias sgr so far. This could be because they don't use english there.
By my guestimate its probably around 3/15 of Kenyas freight cost, if we assume 1unit of power is 3 us cents in ethiopia and 15 us cents in kenya. Labour, capital cost, and maintenance is also higher for kenya diesel SGR.
So if we also assume that kenya sgr will be 8 us cents per ton.km, then ethiopia will be circa 1 us cents per ton.km