Hi,

Adding new filters requires 3 steps : adding the field boxes in the search form, geting the filter and creating the database filter to it.

In this particular case:
1.
Add to t_search.tpl somewhere in the form
Price Range
<input type="textbox" name="price_start" />
<input type="textbox" name="price_end" />
2.Edit com_adsman/models/adsman.php setFiltersList() method
and add:
In the  case:
" if ($reset != "all") "

$filters["price_start"] = JRequest::getVar('price_start', $app->getUserStateFromRequest('com_adsman.price_start','price_start'));
$filters["price_end"] = JRequest::getVar('price_end', $app->getUserStateFromRequest('com_adsman.price_end','price_end'));

and on else:
$app->setUserState('com_adsman.price_start', '');
$app->setUserState('com_adsman.price_end', '');

3.
In the same model file in the buildFiltersQuery() method
add before:
        $this->setState( "where", $where );
these:
        if (!empty($filters["price_start"])) {
            $where[] = " a.askprice >= '" . $filters["price_start"] . "' ";
        }
        if (!empty($filters["price_end"])) {
            $where[] = " a.askprice <= '" . $filters["price_end"] . "' ";
        }

Cheers,
Sorin