Need way to NOT pass price of $0 to Paypal for one product radio button choice

http://www.annepouch.com/providence-swings/class-registration/

On this form, classes are chosen as products with a dropdown. However in order to not have the first option show up as selected, I have added a class option of Not This Time with a price of $0.
Problem is that this shows up as a Product Selection going through to Paypal with a $0 charge.
Its a roundabout solution to solving the problem of using the dropdown where the initial class option that appears in the dropdown is automatically chosen.
Is there a way to either have the dropdown NOT preselect an option OR
to add code in one of the Gravity Form files that will not list Not This TIme as a selection?
Feeling I am missing something here.!
Thanks.
Anne

Thanks Chris. I know it makes no sense to pass a $0 amount to Paypal, you're right.
However I am already using that conditional field for checking the Payment Method field and if they select "Paypal" it goes through to Paypal - the other options is payment by check.

If I could find another way to get through the registration and peel off the Check payers from the Paypal payers before hitting this logic that would be great.

The problem is complicated by the fact that we don't want people to register for 2 Thursday classes so have added the "Not This Time" field so that if one of the thursday classes is chosen, the other selection is hidden. May be the route to the whole problem here we have gotten into.

If you have a product with options in a dropdown box, it seems to automatically select the first option that appears when in fact someone may not want to select that product at all. How can you have it so that a dropdown only appears when a user indicates they want the product?

Thanks!