How to customize a field price in Drupal Commerce?
You might want to try to customize the price via either of these contributed modules that can be used in combination with Drupal Commerce (quotes are from their project pages):


Drupal Commerce Extra Price Formatters (has a stable D7 version):



  This is an add-on module for Drupal Commerce that provides additional options when displaying the formatted price in your store.



Commerce Price FlexyFormatter (DEV version only).



  ... adds more options to format your products price.


Another option is to try what is described in the (accepted) answer to the question about "Additional classes for price based on price components", which includes a template.php tweak and states:


  ... you could theme the price components to add your own classes via a theme override.