mirstiker,
<!Doctype html>
<html>
<head>
<meta charset = "utf-8"/>
<link rel="stylesheet" type="text/css" href="krugki.css">
</head>
<body>
<div class="krugka">
<form action ="" method="POST">
<INPUT type="radio" name="krugka" value="standart" checked="checked"/> Стандартная кружка </br>
<INPUT type="radio" name="krugka" value="xameleon" /> Кружка хамелеон </br>
<INPUT type="radio" name="krugka" value="pivo" /> Кружка пивная </br>
<input type="submit" name="submit" value="Стоимость" />
</form>
</div>
<div>
<img src = "image/standart.jpg">
</div>
<script>
window.addEventListener('DOMContentLoaded', function() {
var img = document.querySelector('img');
[].forEach.call(document.querySelectorAll('input[name="krugka"]'), function(item) {
item.addEventListener('click', function() {
img.src = 'image/' +item.value+ '.jpg';
});
});
});
</script>
</body>
</html>