JSFiddle - React, Tailwind, and code Playground

HTML

<select class="form-select" data-price="5000" data-target="display1">
  <option value="#" selected="selected" disabled="">Выбрать</option>
  <option value="0">Всадной</option>
  <option value="1400">Сквозной (+1400)</option>
  <option value="1000">Цельнометаллический (+1000)</option>
</select>

<pre id="display1"></pre>

<select class="form-select" data-price="3000" data-target="display2">
  <option value="#" selected="selected" disabled="">Выбрать</option>
  <option value="1000">Текстолит (+1000)</option>
  <option value="8000">Латунь (+8000)</option>
  <option value="10000">Титан (+10000)</option>
</select>

<pre id="display2"></pre>

CSS

pre {
  margin: 1em;
  padding: 1em;
  outline: dashed 1px gray;
}

JavaScript

document.querySelectorAll('select.form-select').forEach(select => {
  const display = document.getElementById(select.dataset.target)
  const startPrice = parseInt(select.dataset.price, 10)
  select.addEventListener('change', function() {
    const value = parseInt(this.value, 10)
    display.textContent = startPrice + value
  })
})