[ruslan_mart]

<form name="myForm">
    <input checked="checked" name="check1" type="checkbox">
    <input name="check2" type="checkbox">
    <input name="check3" type="checkbox">
</form>
        
<div id="result"></div>

(function() {
    var form = document.forms.myForm,
        labels = form.elements,
        result = document.getElementById('result');
    
    function onChange() {
        result.innerHTML = labels.check1.checked * 5E5 + labels.check2.checked * 1E5 + labels.check3.checked * 15E4 + 'р.';
    };
    
    form.addEventListener('change', onChange);
    onChange();
    
})();