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
and plugging it in to your router is a good idea. You still need the router to give you a firewall but the switch will give you more ports. I installed one a few months ago and it gives you more ports and speeds up your home network (provided you have gigabit ethernet cards in your computers.)