usebest,
вариант того как я вас понял
<!DOCTYPE HTML>
<html>
<head>
<title>Untitled</title><meta charset="utf-8">
<script type="text/javascript" src="https://ajax.googleapis.com/ajax/libs/jquery/1.11.1/jquery.min.js"></script>
</head>
<body>
<form action="" method="POST">
<input type="text" name="text1" id="text1" class="sum" /><br />
<input type="text" name="text2" id="text2" class="sum" /> <br />
<select name="u1" class="chkOptions">
<option value="0" selected="selected">нет</option>
<option value="120">1 упаковка</option>
<option value="240">2 упаковки</option>
<option value="300">3 упаковки</option>
</select>
<select name="u2" class="chkOptions2">
<option value="0" selected="selected">нет</option>
<option value="121">4 упаковка</option>
<option value="245">5 упаковки</option>
<option value="302">6 упаковки</option>
</select>
<br />
<input type="checkbox" id="chk1" value="400" class="sum" /><label for="chk1">400</label> <br />
<input type="checkbox" id="chk2" value="100" class="sum" /><label for="chk2">100</label> <br />
<input type="checkbox" id="chk3" value="41" class="sale" /><label for="chk3">41%</label> <br />
<input type="checkbox" id="chk4" value="15" class="sale" /><label for="chk4">15%</label> <br />
<input type="checkbox" id="chk5" value="43" class="sale" /><label for="chk5">43%</label> <br />
<input type="checkbox" id="chk6" value="16" class="sale" /><label for="chk6">16%</label> <br />
Итого <input type="text" name="text" id="text">
</form>
<script>
$(function() {
var calc = function() {
var sum = 0;
$("select,.sum[type='text'],.sum:checked", fields).each(function() {
sum += +this.value||0
});
var sale = 0;
$(".sale:checked", fields).each(function() {
sale += +this.value
});
$("#text").val((sum - sum * sale / 100).toFixed(2))
};
fields = $("form");
fields.on('input change',calc)
});
</script>
</body>
</html>