your form uses the get method.
change lines 19 - 20:
$WADbSearch2->addComparison("Price","".WADS_stripCurrency($_POST["S_MinPrice"]) ."","AND",">=",1);
$WADbSearch2->addComparison("Price","".WADS_stripCurrency($_POST["S_MaxPrice"]) ."","AND","<=",1);
to:
$WADbSearch2->addComparison("Price","".WADS_stripCurrency($_GET["S_MinPrice"]) ."","AND",">=",1);
$WADbSearch2->addComparison("Price","".WADS_stripCurrency($_GET["S_MaxPrice"]) ."","AND","<=",1);