<td>
<input type="text" name="count-item" id="count" value="1">
</td>
<span id="cost">52.5</span>
<span id="result"></span>
var cost = document.getElementById('cost');
var count = document.getElementById('count');
var result = document.getElementById('result');
count.addEventListener('change', function() {
result.textContent = parseInt(count.value, 10) * parseFloat(cost.textContent);
});