<?php

function woocommerce_pre_get_posts( $query ) {

  if ( ! is_admin() && is_post_type_archive( 'product' ) && $query->is_main_query() ) {

    // Option 1
    $args = array(
      array(
        'meta_key'  => '_price',
        'value'     => array( 50, 500 ),
        'compare'   => 'BETWEEN'
      )
    );

    // Option 2
    $args = array(
      array(
        'meta_key'  => '_price',
        'value'     => array( 50, 500 ),
        'compare'   => 'BETWEEN',
        'type'      => 'NUMERIC'
      )
    );

    // Option 3
    $args = array(
      'relation' => 'AND',
      array(
        'meta_key'  => '_price',
        'value'     => 50,
        'compare'   => '>=',
      ),
      array(
        'meta_key'  => '_price',
        'value'     => 500,
        'compare'   => '<=',
      )
    );

    $query->set( 'meta_query', $args );
  }
}
add_action( 'pre_get_posts', 'woocommerce_pre_get_posts', 20 );