A wireless router is just a box that you purchase to provide a wireless signal from your existing internet connection. While wireless routers are convenient, they can also be a big hassle. They can be expensive and complicated to set up. Wireless signals sometimes degrade due to many factors giving poor performance. And if you do not know how to protect your wireless signal, someone outside of your home may even be able to connect to your internet connection! Though if you have a large house and are unable to run cables from your Cable modem to your PlayStation, then a wireless router may be for you.
However, if you don't mind running a long cable from your modem to your PlayStation, you could look in to getting an Ethernet switch to essentially "split" your internet connection. They are very inexpensive, small, and easy to setup(Just plug it in to your Cable modem with an Ethernet cable and then plug in your computer/PlayStation to the other slots). Usually they can support up to 4 connections for 1 internet connection and cost as low as $8.
Here is a link to some small cheap ones that should be effective http//www.newegg.com/Product/ProductList.aspx?Submit=ENE&N=2052810030%20115010988&bop=And&Order=PRICE