PMPro Sponsored Members Example with custom callback to override seat pricing.

my_init_override_sponsored_members_pricing_update.php

/**
 * Sponsored Members setup with child seat costs and child fields at checkout.
 */
global $pmprosm_sponsored_account_levels;	
$pmprosm_sponsored_account_levels = array(	
	1 => array(
		'main_level_id' => 1,
		'sponsored_level_id' => 2,
		'seat_cost' => 35,
		'min_seats' => 1,
		'max_seats' => 10,
		'sponsored_accounts_at_checkout' => true,
		'seat_cost_text' => '<br />Total cost will be $200 for 1 seat, $270 for up to 3, $340 for up to 5, $445 for up to 10.',
	)
);

/**
 * Remove Sponsored Members Pricing update and use our own.
 */
function my_init_override_sponsored_members_pricing_update() {
	remove_filter( 'pmpro_checkout_level', 'pmprosm_pmpro_checkout_levels' );
	add_filter( 'pmpro_checkout_level', 'my_custom_pmpro_seat_pricing' );
}
add_action( 'init', 'my_init_override_sponsored_members_pricing_update' );

/**
 * My custom pricing.
 */
function my_custom_pmpro_seat_pricing( $level ) {	
	// Only concerned about level 1
	if ( $level->id != 1 ) {
		return $level;
	}
	
	// get seats from submit
	if ( isset( $_REQUEST['seats'] ) )
		$seats = intval($_REQUEST['seats']);
	else
		$seats = "";
	
	switch ( $seats ) {
		case $seats < 2:
			// use level price
			break;
		case $seats <= 3:
			$level->initial_payment = $level->initial_payment + 70;
			$level->billing_amount = $level->billing_amount + 70;
			break;
		case $seats <= 5:
			$level->initial_payment = $level->initial_payment + 140;
			$level->billing_amount = $level->billing_amount + 140;
			break;			
		case $seats <= 10:
			$level->initial_payment = $level->initial_payment + 245;
			$level->billing_amount = $level->billing_amount + 245;
			break;		
	}
		
	return $level;
}