<html lang="ru">

<head>
    <meta charset="UTF-8" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <meta http-equiv="X-UA-Compatible" content="ie=edge" />
    <title>Document</title>
</head>

<body>
    <div class="container" id="module-calculate-something">
        <form id="field-calculating"><select id="choose-price"><option>Первый выбор</option><option>Второй выбор</option><option>Третий выбор</option><option>Четвёртый выбор</option><option>Пятый выбор</option></select><label for="amount-peoples">Количество людей</label><input
                id="amount-peoples" type="number" min="0" step="1" value="1"/><label for="amount-hours">Количество часов</label><input id="amount-hours" type="number" min="0" max="24" step="1" value="1" /><label for="amount-days">Количество дней</label><input id="amount-days"
                type="number" min="0" step="1" value="1" /></form>
        <div class="price" id="price">Цена 1000</div>
    </div>
</body>

</html>
.price {
  border: 2px solid;
  width: 100px;
  height: 100px;
}



let opCalculateCostSomething = {
    module: document.getElementById(`module-calculate-something`),
    select: document.getElementById(`choose-price`),
    gradPrices: [[1000, 600, 500, 450], [1000, 600, 500, 450], [1500, 800, 700, 600], [1500, 800, 700, 600], [1500, 1500, 1500, 1500]],
    events: {
      input: e => {
      [opCalculateCostSomething.peoples, opCalculateCostSomething.hours, opCalculateCostSomething.days] = [+document.getElementById(`amount-peoples`).value, +document.getElementById(`amount-hours`).value, +document.getElementById(`amount-days`).value];
      opCalculateCostSomething.module.lastElementChild.textContent = ` Цена  ${opCalculateCostSomething.peoples * opCalculateCostSomething.hours * opCalculateCostSomething.days * opCalculateCostSomething.gradPrices[opCalculateCostSomething.select.selectedIndex][opCalculateCostSomething.hours < 2 ? 0 : opCalculateCostSomething.hours >= 2 && opCalculateCostSomething.hours < 4 ? 1 : opCalculateCostSomething.hours >= 4 && opCalculateCostSomething.hours < 7 ? 2 : 3] || `0`}  Р.`;
      }
    }
    };
    opCalculateCostSomething.module.addEventListener(`input`, opCalculateCostSomething.events.input);

External CSS

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External JavaScript

This Pen doesn't use any external JavaScript resources.