Looking to extend network to another building

Hello I am looking for the best, and most cost effective way to extend a network from building to building. Without getting into the nitty gritty my building is currently on a poorly designed subnet of the network itself and the administrators have failed to properly set it all up. I am looking for the best way to expand the network which works perfectly in building A over to building B. there is less than 150 ft between sightlines and that is out of a window from A across a 120 ft field to a window in B which is slightly around the corner from the original window in A. Im thinking distance will not be the issue but cost. Is there a cheap way to receive and repeat the signal and what type of setup or configuration would be involved. I have read briefely of a freeware firmware (WR DDT) perhaps that can do something of this nature but I am looking for as many possible solutions. It has to be neat and discreet. I have an IT guy on my side if I can think of a solution (deniability I guess).