I suggest you purchase a wireless bridge client (preferably of the same brand) to extend the range of your router. However, if you want a cheap (in monetary terms) way to do it you can purchase one or two old Linksys routers on e-bay and flash the memory to
OpenWRT (an open source firmware) and set them up as WiFi bridge repeaters. Here is a
link to detailed instructions on how to accomplish this. They upgrade the attennas and boost the transmit power which would not be required for normal home use.
I use OpenWRT on my home router and it works great. It gives your cheap stock $50 router the capabilities of a router costing $250 or more. But, it is not for the faint hearted and can cause headaches during the set up phase.
If you just want the extra ports, then buying a 5 or 8 port