In your links you need to add in the:
&categories_id=XX

so something like:

Code:
    $content .= '<a href="' . zen_href_link('advanced_search_result&keyword=&pfrom=' . SP_RANGE_3_F . '&pto=' . SP_RANGE_3_T . '&categories_id=' . $_GET['cPath']) . '">' . SP_RANGE_3 . '</a><br />';