you dont need to do the lookup on another page.
You need to set the radio buttons up to pass the id, and use the radio button value in the lookup recordset.
See the "Product Options with eCart" tutorial on the ecart support page, one part of it deals with product options that do not efect price, this is how you currently have it set up. the other part deals with product options that do effect price, this is section walks through having the option form element pass an id to a lookup recordset to get the option name and the price to pass back into the cart, this is how you need to have it set up.