Hide Buying Options if Price = 0

I'd like to alter my single item page to not show any buying options if the price is equal to zero. Is there an easy way to do this, perhaps by editing my custom mp_product.php or this function that I'm using:

function framemarket_product_meta() {
global $post;

//don't filter outside of the loop
if ( !in_the_loop() )
return $content;
$content = '<div class="product-meta-details">';
$content .= mp_category_list($post->ID, '<span class="grid_mp_product_categories">' . __( 'Categories: ', 'mp' ), ', ', '</span>');
$content .= '</div><div class="product-meta-details">';
$content .= $product_price;
$content .= mp_buy_button(false, 'single');
$content .= '</div>';

return $content;
}