if you haven't noticed THATS OPTION 6 of my suggestions.
wireless and thick concrete doesn't mix, theres hardly any other solution to boost signals and most of them compromises too much to achieve one thing.
6) either the best way is to plant wires at the shortest route, through outside is what i think rather than through the door, stairs, back into the door.
7) or put both transmitters nearer the window, the signals would circle outside instead of going through two thick concretes.
7.1) or do it like this via placing the transmitters nearer each other, yes mount it onto the ceiling if you must, oh look i shrunk like 60% more or less of the distance.
and do note, in terms of least costs bare cable > repeater, you're your own labor. see first as to how much would a repeater cost locally, they could potentially reach 50+$ a piece(cheap ones could go as low as 20$, and good strong ones go as far as 100$), more so with multiple repeaters.
if you're willing to spend more than 100$, might as well consider purchasing something else, a
600mW wifi router maybe?
edit: theres also the way of brute force, buying directional bi-quad antennas facing each other through the floors, but of course cancer for the living that goes in between the signals.
although im still waiting for the reply if the airport express supports external antennas, if they do then find out which type of wifi it uses and purchase a matching 12dB antenna and take note of the antenna connector, place the antenna onto a spot which your consoles gets good signal.
