Make Conditional Field work with Price widget
Conditional field module is base on the States API. You can probably do this via a hook_form_alter in a module.

The example below will make the field 'my_field_price' visible and required when 'my_checkbox' is checked.

  $form['my_field_price']['#states'] =&gt; array(
    // Show and make the field required if 'my_checkbox' is checked.
    'visible' =&gt; array(
      ':input[name="my_checkbox"]' =&gt; array('checked' =&gt; TRUE),
    ),
    'required' =&gt; array(
      ':input[name="my_checkbox"]' =&gt; array('checked' =&gt; TRUE),
    ),
  ),