Urgent Cforms ii help needed

I am trying to create a donations form and so far everything worked out well. The only thing im having a problem with is I created a radio group with dollar amounts for people to select. The last radio button i want to label as “Other” and have a text field for them to insert a custom amount in. How do I create that as i can not figure out how to put a text field in the radio group. And after that is done how do i get the text field to update the value. So in the text box if they put $10 i want the amount_value=$10

This is very urgent as our tech guy screwed up our form before he quit.