You would have to customize the payment module(s) where the order status is set to change on orders that have totals >= 50 ...
Example, in Check/Money Order
/includes/modules/payment/moneyorder.php
this code is getting the setting for the Orders Status based on the settings of the Payment Module:
Code:
if ((int)MODULE_PAYMENT_MONEYORDER_ORDER_STATUS_ID > 0) {
$this->order_status = MODULE_PAYMENT_MONEYORDER_ORDER_STATUS_ID;
}
You can change that value of the:
$this->order_status
based on the amount of the order to a different Order Status such as Pending, so the Downloads are not immediately available ...