It depends on whether or not you want phone with the internet service. Without the phone added to the plan, it starts at about 15 dollars a month but if you want a faster downloading speed then it can cost up to 140 dollars.
You do not have to pay for internet service on the iPod Touch. The iPod Touch has a built in Wi-Fi receiver, and as long as there is a router within range (and if it is locked, and you know the WEP...