Fortunately, you don't need to purchase anything. You need to access the administration panel of your router and add a port forward to your local IP address. How to do this depends on your router model but most models are covered at
www.portforward.com.
I added this to the FAQ:
1. Select your router from the list of routers on the first page of
www.portforward.com.
(Routers usually have a sticker with its name and model number printed on it.)
2. After selecting router click the Default Guide link in the text area at the top.
3. Follow the instructions to forward port 6260 to your computer.
I hope that makes it a little clearer.