Don't know what you mean about negative cost facilities, but negative monthly cost does exactly what you expect - free cash every month!
Also, GIMP works fine if you know what settings to use. Find copies of the proper palette files (I remember finding them somewhere on the forum in a photoshop thread), put them in GIMP's palette folder. Then, make a new image, go to Image->Mode->Indexed, and in the dialogue box choose the XCom palette you want and untick the option for removing unused colors. It's a good idea to save a project file with this as a template, so you always start with the correct settings.