Reversato,
<!DOCTYPE HTML>
<html>
<head>
<title>Untitled</title>
<meta charset="utf-8">
<style type="text/css">
</style>
<script src="http://ajax.googleapis.com/ajax/libs/jquery/1.11.0/jquery.min.js"></script>
<script>
$(function() {
var price = 0;
var span = $('span');
span.html(price);
var arr = [100, 200, 300];
$('#select').change(function() {
price = arr[this.selectedIndex]
span.html(price);
})
});
</script>
</head>
<body>
<span></span>
<select name="select" id="select">
<option value="1">Значение 1</option>
<option value="2">Значение 2</option>
<option value="3">Значение 3</option>
</select>
</body>
</html>