Adding priced options to products in Drupal Commerce
Oh and no - I didn't set the term reference field to unlimited values because I only want them to pick one value from the list


I believe that is the problem... either you make it unlimited; even though, you will use it once 

OR leave it at 1, but don't use a loop, just add action (for Amount Value data selection use commerce-line-item:field-price:amount)