My code is as follows - also available as an attachment below:
<?php
include_once(drupal_get_path('module', 'webform') .'/includes/webform.submissions.inc');
$nid = arg(1); // need to hard-code nid if this is a custom page
$sid = $_GET['sid']; $submission = webform_get_submission($nid, $sid);
$invoice_numbers = $submission->data[3][0]; // 3 is the ID number of the field for invoice numbers under form components
$amount = $submission->data[4][0]; // 4 is the ID number of the amount field under form components
?>
<h2>Confirmation</h2>
<ul>
<li>Click "Buy Now" to finalize your registration.</li>
<li> Important: Print out your PayPal payment as a receipt.</li> </ul>
<h4> Amount: $<?php print $amount; ?></h4>
<form action="https://www.paypal.com/cgi-bin/webscr" method="post">
<input name="cmd" type="hidden" value="_xclick" />
<input name="business" type="hidden" value=“This email address is being protected from spambots. You need JavaScript enabled to view it.“ />
<input name="item_name" type="hidden" value="Payment on Invoice <?php print $invoice_numbers; ?>" />
<input name="item_number" type="hidden" value="SKU0123" />
<input name="amount" type="hidden" value="<?php print $amount; ?>" />
<input name="bn" type="hidden" value="PP-BuyNowBF:btn_buynowCC_LG.gif:NonHostedGuest" />
<input style = "width: 120px; height: auto;" alt="PayPal - The safer, easier way to pay online!" border="0" name="submit" src="https://www.paypalobjects.com/en_US/i/btn/btn_buynowCC_LG.gif" type="image" />
<img alt="" border="0" height="1" src="https://www.paypalobjects.com/en_US/i/scr/pixel.gif" width="1" /></form>
