$args = array(
'post_type' => 'product',
'meta_query' => array(
array(
'key' => 'usluga',
'value' => 1,
),
array(
'key' => 'price',
'value' => array( 100, 500 ),
'type' => 'numeric',
'compare' => 'BETWEEN'
)
)
);
$query = new WP_Query( $args );