Just back from Rwanda, may I warmly recommend you (we stayed there five nights) the MOTEL STEP TOWN , located close to the centre (KN 1 , a few minutes by car) of Kigali.
Price for a normal single room is 50 Dollar, for a double 55 Dollar.
There is a good restaurant, people are very helpful and hotel is very clean and
we enjoyed a beautiful view from the hillside.
They also have a website http://step-town.com