Why not use WDS on cheapo firmware-hacked routers, using dd-wrt/openWRT/freeWRT (I use Tomato)? If you really want speed, you may be able to find standard 802.11n routers that can do WDS, although if I really wanted speed I would (and do) use cable. These firmwares usually also allow wireless strength mods, although it may not be practial.
For info on WDS: http://en.wikipedia.org/wiki/Wireless_Distribution_System or: http://www.dd-wrt.com/wiki/index.php?title=WDS_Linked_router...