qumo,
<!DOCTYPE html>
<html>
<head>
<title>Untitled</title>
<meta charset="utf-8">
<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.12.4/jquery.min.js"></script>
<script>
$(function() {
var price = document.getElementById('answer'),
ems_price = 2200;
price.innerHTML = ems_price;
function question() {
var method = $('.find').val();
switch(method) {
case 'ems':
var weight = +$('#weight').val();
var sum = ems_price;
if(weight > 0.5 && weight <= 1){
for (var i= 5 ; i< weight*10; i++) {
sum += 200
};
};
price.innerHTML = sum;
break;
//Далее тоже расчет по формулам будет=))
case 'avia':
price.innerHTML = avia_price;
break;
case 'sal':
price.innerHTML = sal_price;
break;
case 'parohod':
price.innerHTML = parohod_price;
break;
}
}
$('#weight').on("input", question);
$('.find').on("change", question);
});
</script>
</head>
<body>
<select name="method" class="find" >
<option value="ems">ЕМS</option>
<option value="avia">Авиа</option>
<option value="sal">SAL</option>
<option value="parohod">Пароход</option>
</select>
<input type="number" value="0.5" min="0.5" step="0.1" max="1" name="weight" id="weight" size="4" >
<hr><span id="answer"></span> руб
</body>
</html>