$(".plus").click(function() {
var $price1 = document.createElement("INPUT");
$price1.setAttribute("value", "<?= $arResult['CATALOG_MEASURE_RATIO'] ?>");
//$price1.setAttribute("type", "text");
console.log($price1);
var summa = $("#cena_tovara");
var summaTov = summa.text();
console.log(summaTov);
var valueSum = $price1 * summaTov;
$('.result').text(valueSum);
});
<div class="itogo">
Цена: <span id="cena_tovara">1500</span>
Итого: <span class="result"></span>
</div>
<div class="amount">
<div class="val">
<a href="#" class="minus"></a>
<input type="text" value="<?= $arResult['CATALOG_MEASURE_RATIO'] ?>" data-minimum="<?= $arResult['CATALOG_MEASURE_RATIO'] ?>" data-maximum="9999" data-step="<?= $arResult['CATALOG_MEASURE_RATIO'] ?>" class="input" maxlength="4">
<a href="#" class="plus"></a>
</div>
</div>
<script>
$(".plus").click(function() {
var $price1 = document.createElement("INPUT");
$price1.setAttribute("value", "<?= $arResult['CATALOG_MEASURE_RATIO'] ?>");
var summa = $("#cena_tovara");
var valueSum = $price1 * summa;
$('.result').text(valueSum);
});
</script>