mastersss,
<!DOCTYPE HTML>
<html>
<head>
<title>Untitled</title>
<meta charset="utf-8">
</head>
<body>
<input id="field_54ef5f88727d7_200_field_54ef5f88727da">
<input id="field_54ef5f88727d7_2_field_54ef5f88727da">
<input id="field_54ef5f88727d7_7_field_54ef5f88727da" value="test">
<script>
alert(document.querySelector('[id^="field_54ef5f88727d7_"]:last-of-type').value);
</script>
</body>
</html>