wmfmynd,
<!DOCTYPE HTML>
<html>
<head>
<title>Untitled</title>
<meta charset="utf-8">
<style type="text/css">
</style>
<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.12.0/jquery.min.js"></script>
<script>
$(function(){
var d = 20.45;
$(".radio").each(function(){
var res = ($(".dollar",this).html()*d*100|0)/100;// или через .toFixed(2)
$(".br-result",this).html(res)
});
})
</script>
</head>
<body>
<table class="size">
<tbody>
<tr>
<th>Размер</th>
<th>Стоимость</th>
</tr>
<tr id="convertid-1" class="radio r-id-2">
<td>80x43x8мм</td>
<td><span class="br-result"></span> руб. ($<span class="dollar">2.6</span>)</td>
</tr>
<tr id="convertid-2" class="radio r-id-2">
<td>120x65x12мм</td>
<td><span class="br-result"></span> руб. ($<span class="dollar">5.89</span>)</td>
</tr>
<tr id="convertid-3" class="radio r-id-1">
<td>180x97x18мм</td>
<td><span class="br-result"></span> руб. ($<span class="dollar">13.35</span>)</td>
</tr>
</tbody>
</table>
</body>
</html>