I don't have a router, I have a wireless gaming adapter for an xbox. And it's safer to have a router because then there is a break between your internetz and the cable modem. (some people say you can get spied on through your modem)
It's safer because it's generally really easy to go straight to your comp from the modem. And it's also helpful because you can have multiple things plugged in, instead of switching it out 1000 times. Like ty said you could have a wired router, or one that has wireless also. Wired would obviously make you plug in with wires, while wireless can do both but for a bit more $$ (and you need a wireless thing for the xbox).
$20 + $3-5 shipping through Paypal, that way I could have USPS track it for you so you know you're not getting screwed. And Paypal would handle the money. Ebay would be ridiculous because they charge seller fees and listing fees. (I'll PM you my wife and I's Ebay ID so you can check the feedback if you want) Just so you know, it's a Belkin Wireless G gaming adapter, it uses the ethernet connection on your xbox to provide wireless support for your xbox to router. It has auto detect features that work with almost any router. It retails at $60 I only had it plugged in for like 2 months then got an official xbox one from a friend. let me know what you think and I'll PM you details if you want to go through with it.