Limit currency for one product in Drupal Commerce
I'm afraid there's no custom module for this, you'll need to alter the product form add/create to adapt to your settings/conditions (simplified logic below):

/**
 * Implements hook_form_FORM_ID_alter().
 */
function my_module_commerce_form_commerce_product_ui_product_form_alter(&amp;$form, &amp;$form_state, $form_id) {
  // Calculate the currency for a given product.
  $currency_code = 'USD';
  $form['commerce_price'][LANGUAGE_NONE][0]['currency_code']['#type'] = 'value';
  $form['commerce_price'][LANGUAGE_NONE][0]['currency_code']['#default_value'] = $currency_code;
  $form['commerce_price'][LANGUAGE_NONE][0]['amount']['#field_suffix'] = $currency_code;
}


A more complex and customizable option would be to use hook_field_widget_info_alter and modify the settings form to add whatever conditions you want for selecting a currency on a product form.