I think the problem here is in the fact that you dont want to spend money ! I have given options in this debate along with others with regard to repeaters, Ethernet over power adaptors, ect, whithout spending money, now its time to spend some effort !
I agree with previous post, get a longer cable, make one or join 2 together.
You last resort is this ! You need to remember that Wi-Fi is a sort of '2 wall technology' once its gone through 2 walls its in trouble ! Wi-Fi does not like building structure, so if your 'short cable' cable is long enough to get through a wall in the right direction that you want to extend range, drill a hole in the wall and connect the 2 routers, you may be surprised what happens !