Евгений Фоменко,
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<html>
<head>
<title>Untitled</title>
<meta charset="utf-8">
<style type="text/css">
</style>
<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.12.4/jquery.min.js"></script>
<script>
$(function() {
var str = $('[data-role="carttotal"] span').text();
str = str.replace(/\D/g,'');
alert(str);
});
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<body>
<div data-role="cartbonus" style="text-align: left;">Бонус: <span>50 руб</span></div>
<div data-role="carttotal" style="text-align: left;">Итого: <span>750 руб</span></div>
</body>
</html>