Hello sir, I can help you. Since you've declared the option you need does not relate to shipping method, are you going to extend the Checkout functionality itself? Then I'm afraid the price will not be as low as your expectations as this requires for much more work than just a couple of hours.
Could you please describe more exactly what are the radioboxes you need, what are they for, how should they interact with other page elements, and how should they be seen in the order? If the things are really simple, I can adjust my bid to actual budget.
Regards, Victor