Here is example from Codex on using BETWEEN
with new format of meta query, which covers multiple fields as well:
$args = array(
'post_type' => 'product',
'meta_query' => array(
array(
'key' => 'color',
'value' => 'blue',
'compare' => 'NOT LIKE'
),
array(
'key' => 'price',
'value' => array( 20, 100 ),
'type' => 'numeric',
'compare' => 'BETWEEN'
)
)
);
$query = new WP_Query( $args );
See Custom Field Parameters for details.