I would use the switch statement using the value of the radio button group to make the selection. This will allow for multiple items to have the price.
// set price based on the value of the radio buttons;
case "Off" :
// no item selected;
event.value = "";
case "1" :
// item one;
event.value = 0.10;
case "2" :
case "3" :
// item 2 and 3 have the same price;
event.value = .20;
// item with no price value;
app.alert"Missing price for item with value of : " + this.getField("RadioButtonField").value, 1, 0);
1. The code you have mentioned - does I insert it in the Script Editor after I selected the text field?
2. You say each radio button have to have the same name? I don't understand. I have one group, it has four radio buttons with different names and values. By name, are you referring to the actual radio button label or another name?