Psy Diamond,
<!DOCTYPE HTML>
<html>
<head>
<title>Untitled</title>
<meta charset="utf-8">
</head>
<body>
<div>
<select id="sel" onchange="foo()"><option value="1"></option>
<option value="2">Белый</option>
<option value="3">Серый</option>
<option value="4">Желтый</option>
<option value="5">Ораньжевый</option>
<option value="6">Синий</option>
<option value="7">Черный</option>
</select>
</div>
<div>
<input id="kol-vo" oninput="foo()" type="text" value="0" />
</div>
<div id="result">0</div>
<script>
var ratio = {1:0,2:500,3:500,4:500,5:700,6:700,7:700};
function foo()
{
var num = +document.getElementById('kol-vo').value||0,
indx = +document.getElementById('sel').value;
document.getElementById('result').innerHTML = num * ratio[indx]
}
</script>
</body>
</html>