JSFiddle - React, Tailwind, and code Playground

HTML

<div class="goods">
    <div class="name">Название товара</div>
    <div class="goods-count">
        <span class="amount">
            <input type="button" class="down" value="-">
            <input type="text" class="counter" value="1" size="4" data-price="5000" data-count="1"> шт
            <input type="button" class="up" value="+">
        </span>
    </div>
    <div class="goods-price"><span class="sum">5000 руб.</span></div>
</div>

JavaScript

$(document).ready(function() {
  var counterSel = $('.counter');
  var sumSel = $('.sum');
  var unitPrice = counterSel.attr('data-price') / counterSel.attr('data-count');
  var getCount = function() {
    var result = parseInt(counterSel.val());
    if (isNaN(result)) return 0;
    if (result < 0) return 0;
    return result;
  }
  var updatePrice = function() {
    var totalPrice = getCount() * unitPrice;
    sumSel.html(totalPrice + ' руб.');
  };
  var increment = function(count) {
    var newCount = getCount() + count;
    if (newCount < 0) newCount = 0;
    counterSel.val(newCount);
    updatePrice(); 
  }
  counterSel.on('change', updatePrice);
  counterSel.on('keyup', updatePrice);
  $('.down').on('click', function() {
    increment(-1);
  });
  $('.up').on('click', function() {
    increment(1);
  });
});