JSFiddle - React, Tailwind, and code Playground

HTML

<div id="calc_div">

    <div id="quantity_div"><p class="c">
        Сколько километров <br>
        <input type="text" id="count_inp"><br>
    </div>

    <div id="final_div">
        <p class="c"><button id="process_all_b" >Посчитать</button><br></p>
        <div id="result"><p class="c">0 Рублей</p></div>
    </div>
</div>

JavaScript

$(function() {
  function count() {
    var
    	a = 2000,
      b = 5000,
      c = 30000,
      sum = +$("#count_inp").val() || 0,
      cost = 0,
      $result = $("#result p");

    if (sum <= a) {
      cost = sum * 1.5;
    } else if (sum > a && sum <= b) {
      cost = sum + 1.3;
    } else if (sum > b && sum <=c) {
      cost = sum;
    } else {
      cost = sum * .8;
    }
    
    renderCost(cost)
  }
  
  function renderCost(value) {
  	$("#result p").html(value === 0 ? 'Укажите расстояние' : value + " Рублей")
  }

  var s = $("#process_all_b");
  s.click(count)
});