change_membership_price_by_option.php

<?php

function my_pmprorh_init_2()
{
    //don't break if Register Helper is not loaded
    if(!function_exists("pmprorh_add_registration_field"))
    {
        return false;
    }

    $fields = array();

	$fields[] = new PMProRH_Field(
		'gallery_page',
		'checkbox',
		array(
			'label' => 'Add Gallery Page',
			'profile' => true,
		)
	);

	//add the fields into a new checkout_boxes are of the checkout page
    foreach($fields as $field)
        pmprorh_add_registration_field(
            "checkout_boxes", // location on checkout page
            $field            // PMProRH_Field object
        );
    //that's it. see the PMPro Register Helper readme for more information and examples.
}
add_action("init", "my_pmprorh_init_2");



/*
  If a user checked option1, then add $100 to the price.
*/
function my_pmpro_checkout_level($level)
{
  if(!empty($_REQUEST['gallery_page'])){
	  if($level->id == 1)
	  {
	    $level->initial_payment = $level->initial_payment + 18;
	    $level->billing_amount = $level->billing_amount + 18;	//to update recurring payments too
	  } elseif ($level->id == 2) {
	  	$level->initial_payment = $level->initial_payment + 4.50;
	    $level->billing_amount = $level->billing_amount + 4.50;	//to update recurring payments too
	  } else {
	  	$level->initial_payment = $level->initial_payment + 1.50;
	    $level->billing_amount = $level->billing_amount + 1.50;	//to update recurring payments too
	  }
}
 
  return $level;
}
add_filter("pmpro_checkout_level", "my_pmpro_checkout_level");