autoship_create_scheduled_order_item_product_price

Can be used to modify the regular price for an order, and takes the following parameters: 

1. Price
2. Frequency
3. Frequency Type
4. WC Product object as parameters.

Example

// change product price based on more frequent ordering
function xx_discount_based_on_frequency ($item_price, $frequency_type, $frequency,$product) {
    if($frequency_type == 'Weeks' && ($frequency == 1 || $frequency == 2)){
        $item_price = $item_price - ($item_price * .10);
    }
    if($frequency_type == 'Weeks' && $frequency == 3 ){
        $item_price = $item_price - ($item_price * .05);
    }
    return $item_price;
}
add_filter('autoship_create_scheduled_order_item_product_price', 'xx_discount_based_on_frequency', 10, 4);