It probably won't be the same, because the sorting is done after the relevance search as a post-process.
It is unfortunately not possible to sort the query by a custom field value without changing the source code. If you use the regular engine, then you can try the following:
1. Open up the wp-content\plugins\ajax-search-pro\includes\classes\search\class-asp-search-cpt.php file and go to line 328:
$priority_select AS priority,
2. ..and change that line to:
(SELECT IF(meta_value IS NULL, 0, meta_value) FROM $wpdb->postmeta WHERE $wpdb->postmeta.meta_key='_price' AND $wpdb->postmeta.post_id=$wpdb->posts.ID) AS priority,
However this will still not guarantee the same results, but it should be different from the current a bit.Best,
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