Adjust pricing for membership level according to selection of Custom Fields in Paid Memberships Pro.

change-monthly-fee-pmpro.php

<?php

/**
 * This will allow you to charge additional extras on the user's monthly membership fee.
 * Copy the code below into your PMPro Customizations Plugin - https://www.paidmembershipspro.com/create-a-plugin-for-pmpro-customizations/
 */
 
 //we have to put everything in a function called on init, so we are sure Register Helper is loaded
function my_pmprorh_init()
{
	//don't break if Register Helper is not loaded
	if(!function_exists( 'pmprorh_add_registration_field' )) {
		return false;
	}
	
	//define the fields
	$fields = array();
	$fields[] = new PMProRH_Field(
		'expert',						// input name, will also be used as meta key
		'checkbox',							// type of field
		array(
			'label'		=> 'Add $175/mo',		// custom field label
			'levels'	=> array(1)
		)
	);

	$fields[] = new PMProRH_Field(
		'research',						// input name, will also be used as meta key
		'checkbox',							// type of field
		array(
			'label'		=> 'Add $95/mo',		// custom field label
			'levels'	=> array(1)
		)
	);

	$fields[] = new PMProRH_Field(
		'complete_upgrade',						// input name, will also be used as meta key
		'checkbox',							// type of field
		array(
			'label'		=> 'Add $270/mo',		// custom field label
			'levels'	=> array(1)
		)
	);


	$fields[] = new PMProRH_Field(
		'expert_2',						// input name, will also be used as meta key
		'checkbox',							// type of field
		array(
			'label'		=> 'Add $200/mo',		// custom field label
			'levels'	=> array(2)
		)
	);

	$fields[] = new PMProRH_Field(
		'research_2',						// input name, will also be used as meta key
		'checkbox',							// type of field
		array(
			'label'		=> 'Add $145/mo',		// custom field label
			'levels'	=> array(2)
		)
	);

	$fields[] = new PMProRH_Field(
		'complete_upgrade_2',						// input name, will also be used as meta key
		'checkbox',							// type of field
		array(
			'label'		=> 'Add $350/mo',		// custom field label
			'levels'	=> array(2)
		)
	);
	
	//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' );


function my_pmpro_checkout_level($level)
{
  if ( ! empty( $_REQUEST['expert'] ) ) {
    // $level->initial_payment = $level->initial_payment + 175; //to update the initial payment.
    $level->billing_amount = $level->billing_amount + 175;	//to update recurring payments too
  }

  if ( ! empty( $_REQUEST['research'] ) ) {
    $level->billing_amount = $level->billing_amount + 95;	//to update recurring payments too
  }

  if ( ! empty( $_REQUEST['complete_upgrade'] ) ) {
    $level->billing_amount = $level->billing_amount + 270;	//to update recurring payments too
  }

  if ( ! empty( $_REQUEST['expert_2'] ) ) {
    $level->billing_amount = $level->billing_amount + 200;	//to update recurring payments too
  }

  if ( ! empty( $_REQUEST['research_2'] ) ) {
    $level->billing_amount = $level->billing_amount + 145;	//to update recurring payments too
  }

   if ( ! empty( $_REQUEST['complete_upgrade_2'] ) ) {
    $level->billing_amount = $level->billing_amount + 350;	//to update recurring payments too
  }
 
  return $level;
}
add_filter( "pmpro_checkout_level", "my_pmpro_checkout_level" );

Hi, doesn't this need a add_filter( "pmpro_checkout_level", "my_pmpro_checkout_level" ); at the end ?

Thanks @sensemonster, I have updated the gist.