SELECT * FROM `database` WHERE `brand` LIKE "%' . $brand . '%" AND `type` LIKE "%' . $type. '%" AND `price` LIKE "%' . $price . '%"

AND `price` LIKE "*";

<?php
$sql = 'SELECT * FROM `database`';
$where = array();
if ($brand !== '') $where[] = '`brand` LIKE "%'.$brand.'%"';
if ($type !== '')  $where[] = '`type` LIKE "%'.$type.'%"';
if ($price !== '') $where[] = '`price` LIKE "%'.$price.'%"';
if (count($where) > 0) {
  $sql .= ' WHERE '.implode(' AND ', $where);
} else {
  // Error out; must specify at least one!
}
// Run $sql

<?php
    $fields = array(
        // Form    // SQL
        'brand' => 'brand',
        'type'  => 'type',
        'price' => 'price',
    );

    $sql  = 'SELECT * FROM `database`';
    $comb = ' WHERE ';
    foreach($fields as $form => $sqlfield)
    {
        if (!isset($_POST[$form]))
            continue;
        if (empty($_POST[$form]))
            continue;
        // You can complicate your $fields structure and e.g. use an array
        // with both sql field name and "acceptable regexp" to check input
        // ...

        // This uses the obsolete form for mysql_*
        $sql .= $comb . $sqlfield . ' LIKE "%'
             . mysql_real_escape_string($_POST[$form])
             . '"';
        /* To use PDO, you would do something like
             $sql .= $comb . $sqlfield . 'LIKE ?';
             $par[] = $_POST[$form];
        */
        $comb = ' AND ';
    }
    // Other SQL to go here
    $sql .= " ORDER BY brand;";

    /* In PDO, after preparing query, you would bind parameters
       - $par[0] is value for parameter 1 and so on.
       foreach($par as $n => $value)
           bindParam($n+1, '%'.$value.'%');
    */