lif3ar,
если слово это 3 и более букв
<!DOCTYPE HTML>
<html>
<head>
<title>Untitled</title>
<meta charset="utf-8">
</head>
<body>
<script type="text/javascript">
var price = 400;
function countChar() {
var is_probel = document.getElementById("is_probel");
var count_char = document.getElementById("count_char");
var count_char_textarea = document.getElementById("count_char_textarea");
var price_out = document.getElementById("price_out");
var len = count_char_textarea.value.match(/[а-яёa-z]{3,}/ig);
len = len ? len.length : 0;
count_char.value = len;
price_out.innerHTML = (len / 1000 * price).toFixed(2);
}
</script>
<div id="count_char_block">
<textarea id="count_char_textarea" style="width: 600px;height: 300px;" oninput="countChar()"></textarea>
<br/>
<input type="text" id="count_char" value="0" readonly="readonly" />
<div>Стоимость составит: <span id="price_out">0</span> руб.</div>
</div>
</body>
</html>