How to query two meta fields and display results between them

You will need to use the meta_query variable like so:

$start = time(); //Now
$end= strtotime('+1 month'); //1 month ahead

query_posts(
    'post_type' => 'event',
    'post_status' => 'publish',
    'posts_per_page' => '10',
    'meta_query' => array(
        array('key' => $prefix.'event_start_timestamp', 'value' => $start, 'compare' => '>=', 'type' => 'NUMERIC'),
        array('key' => $prefix.'event_end_timestamp', 'value' => $end, 'compare' => '<=', 'type' => 'NUMERIC')
    )
);