AdaWiki

add these lines

define('MODULE_SHIPPING_USPS_LIMIT_ERROR', 'For packages over $200 we require shipment via UPS');
define('MODULE_SHIPPING_USPS_LIMIT', 200);

Change 200 to whatever you want the limit to be!

Find line 188

    if (is_array($uspsQuote)) {

and replace with

if (is_array($uspsQuote) && $_SESSION['cart']->total < MODULE_SHIPPING_USPS_LIMIT) {

Find line 281

elseif ($uspsQuote == -1) {
      $this->quotes = array('module' => $this->title,
                            'error' => MODULE_SHIPPING_USPS_TEXT_SERVER_ERROR . (MODULE_SHIPPING_USPS_SERVER=='test' ? MODULE_SHIPPING_USPS_TEXT_TEST_MODE_NOTICE : ''));
    } 

and replace with

elseif ($uspsQuote == -1) {
      $this->quotes = array('module' => $this->title,
                            'error' => MODULE_SHIPPING_USPS_TEXT_SERVER_ERROR . (MODULE_SHIPPING_USPS_SERVER=='test' ? MODULE_SHIPPING_USPS_TEXT_TEST_MODE_NOTICE : ''));
    } elseif ($_SESSION['cart']->total > MODULE_SHIPPING_USPS_LIMIT) {
      $this->quotes = array('module' => $this->title,
                            'error' => MODULE_SHIPPING_USPS_LIMIT_ERROR);
    }

Make sure that you have other shipping options enabled! Don't disable USPS without any good alternatives.

Also, UPS can't ship to PO Boxes. If shipping expensive things to PO Boxes is important for your business, don't do this mod!