From my catalog page customer gets directly to onepage checkout.

My simple product got options which should affect price. This what I'm trying to do: 1. show options (the selection itself) on checkout page. 2. update total when any option is selected. (as its done on product view page)

This seems to be the solution using ajax, but i just cant figure out, how to set everything up. Friends, can anyone explain the thing to beginner?