<table style = "border: 1px solid black; width: 500px;">
    <tr>
        <td style = "background-color: #bbbbbb;"><b>Услуга</b></td>
        <td style = "background-color: #bbbbbb;"><b>Стоимость</b></td>
        <td style = "background-color: #bbbbbb;"><b>Количество</b></td>
    </tr>
    <tr>
        <td>Услуга 1</td>
        <td><span id = "price_1">500</span> ₽</td>
        <td><input id = "amount_1" type = "number" value = "0" placeholder = "Количество" onchange = "funcResult()"/></td>
    </tr>
    <tr>
        <td>Услуга 2</td>
        <td><span id = "price_2">450</span> ₽</td>
        <td><input id = "amount_2" type = "number" value = "0" placeholder = "Количество" onchange = "funcResult()"//></td>
    </tr>
    <tr>
        <td>Услуга 3</td>
        <td><span id = "price_3">1245</span> ₽</td>
        <td><input id = "amount_3" type = "number" value = "0" placeholder = "Количество" onchange = "funcResult()"//></td>
    </tr>
</table>

<b>Итоговая сумма:</b> <span id = "result">0</span> ₽ &nbsp;<input type = "button" value = "Сбросить" onclick = "funcReset()" />

<script>
    const MAX_PRICES = 4; //Максимальное количество услуг
    function funcResult() //рассчитать сумму
    {
        var result = 0;

        for(var pos = 1; pos < MAX_PRICES; pos++)
        {
            if(document.getElementById('amount_' + pos).value < 0)
                document.getElementById('amount_' + pos).value = 0;

            result += document.getElementById('price_' + pos).innerHTML * document.getElementById('amount_' + pos).value;
        }
        document.getElementById('result').innerHTML = result;
    }
    function funcReset() //сбросить данные
    {
        document.getElementById('result').innerHTML = '0';

        for(var pos = 1; pos < MAX_PRICES; pos++)
            document.getElementById('amount_' + pos).value = 0;
    }
</script>