Custom Register Helper fields for Irishhealer thread on price-adjusting fields.

irishhealer_adjust_price_pmprorh_init.php

<?php
/**
 * Custom Register Helper fields for Irishhealer thread on price-adjusting fields.
 */
function irishhealer_adjust_price_pmprorh_init() {
	// Don't break if Register Helper is not loaded.
	if ( ! function_exists( 'pmprorh_add_registration_field' ) ) {
		return false;
	}

	$fields = array();
	$fields[] = new PMProRH_Field(
		'additional_adults',
		'text',
		array(
			'label' => 'Number of Adults (+30€)',
			'levels' => array( '3' ),
			'memberslistcsv' => true,
			'profile' => 'admin_only',
	) );
	$fields[] = new PMProRH_Field(
		'additional_juniors',
		'text',
		array(
			'label' => 'Number of Juniors (+10€)',
			'levels' => array( '3' ),
			'memberslistcsv' => true,
			'profile' => 'admin_only',
	) );

	// Add the fields into a new checkout_boxes are of the checkout page.
	pmprorh_add_checkout_box( 'family', 'Family Details' );

	foreach ( $fields as $field ) {
		pmprorh_add_registration_field(
			'family',
			$field
		);
	}
}
add_action( 'init', 'irishhealer_adjust_price_pmprorh_init' );

/**
 * If a user added adults or juniors options, then adjust the price.
 *
 * @param  object $level The level bobject being purchased at checkout.
 */
function irishhealer_adjust_price_pmpro_checkout_level( $level ) {
	if ( ! empty( $_REQUEST['additional_adults'] ) ) {
		$additional_adults = $_REQUEST['additional_adults'];
		$level->initial_payment = $level->initial_payment + ( intval( $additional_adults ) * 30 );
		$level->billing_amount = $level->billing_amount + ( intval( $additional_adults ) * 30 );
	}
	if ( ! empty( $_REQUEST['additional_juniors'] ) ) {
		$additional_juniors = $_REQUEST['additional_juniors'];
		$level->initial_payment = $level->initial_payment + ( intval( $additional_juniors ) * 10 );
		$level->billing_amount = $level->billing_amount + ( intval( $additional_juniors ) * 10 );
	}
	return $level;
}
add_filter( 'pmpro_checkout_level', 'irishhealer_adjust_price_pmpro_checkout_level' );