Ethernet cables?

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Monoprice.com provides high quality ethernet cables at extremely reasonable prices. 100' CAT 6 cables with molded ends are under $12.

Your best bet at this time is to get CAT 6 cables. If you are running it through attic spaces it needs to be plenum grade.

You do NOT need your wireless router to be as high as possible. Generally, the router will broadcast in a 360 degree sphere. You would actually be better off putting your router in the basement and then shielding it with heavy aluminum foil in all directions in which you do not have devices trying to pick up signal. So if it was on the ground floor or basement and you didn't have any devices below it, placing foil underneath it would protect it from any signals coming from that direction and reflect the portion of your signal going in that direction back up, thereby strengthening your upwards signal while blocking interference from below you. If all your WiFi devices are east of the router, place foil or other reflective surface to the west of the router, etc.