edit line 39 and 40:
$WADbSearch1->addComparison("list_price","".WADS_stripCurrency($_POST["start_price"]) ."","AND",">=",1);
$WADbSearch1->addComparison("list_price","".WADS_stripCurrency($_POST["end_price"]) ."","AND","<=",1);
to:
$WADbSearch1->addComparison("replace(list_price, ',' , ''","".WADS_stripCurrency($_POST["start_price"]) ."","AND",">=",1);
$WADbSearch1->addComparison("replace(list_price, ',' , ''","".WADS_stripCurrency($_POST["end_price"]) ."","AND","<=",1);