ufaclub,
Вариант без js
<!DOCTYPE HTML>
<html>
<head>
<title>Untitled</title>
<meta charset="utf-8">
<style type="text/css">
.item div {
display: none;
}
[name="30sm"]:checked ~ [id="30s"] {
display: block;
}
[name="40sm"]:checked ~ [id="40s"] {
display: block;
}
</style>
</head>
<body>
<div class="item">
<input type="radio" name="30sm" value="30 сантиметров"> 30 см.<br>
<input type="radio" name="40sm" value="40 сантиметров"> 40 см.<br>
<div id="30s">цена за 30см</div>
<div id="40s">цена за 40см</div>
</div>
<div class="item">
<input type="radio" name="30sm" value="30 сантиметров"> 30 см.<br>
<input type="radio" name="40sm" value="40 сантиметров" checked> 40 см.<br>
<div id="30s">цена за 30см</div>
<div id="40s">цена за 40см</div>
</div>
</body>
</html>