Form #states visible for numeric values
Try this:

$form['design']['#states'] = array(
  'visible' =&gt; array(
    ':input[name="price"]' =&gt; array('!value' =&gt; 'other'),
  ),
);


though, to be honest I'm much more a fan of:

$form['design']['#states'] = array(
  'invisible' =&gt; array(
    ':input[name="price"]' =&gt; array('value' =&gt; 'other'),
  ),
);


Here are some good examples to follow. Not exactly your case, but close.