What kind/model of router are you using? Some routers have the capability of being "repeaters" with each other, and you might find a used or recondition one for yours. I have two Netgear's. One hooked to my cable modem that is the base and another as a repeater.
Another way if your router uses external antennas, you may be able to find replacement ones that have a higher "gain" than the one (s) that are on it now.
Edit: Just read the above responses and if your router is on the same channel as others that are near you, that can cause "conflicts" and your range can be cut short.
Here are two free programs that you can use to "see" what is going on around you and then you can switch to a better channel. The auto shift on most routers really do not work that well.
Google for: Vistumbler and inSSIDER and run ether or both to check your radio traffic in your area.
Last edited by DustyDisks; 12-23-2012 at 10:24 AM.