JSFiddle - React, Tailwind, and code Playground

HTML

<script src="https://code.jquery.com/jquery-3.2.1.min.js"></script>
<select>
    <option value="7827 руб">80x190/200см</option>
    <option value="8768 руб">90x190/200см</option>
    <option value="11271 руб">120x190/200см</option>
</select>

<p>Цена матраса: <span id="price"></span></p>

CSS

#price {
    color: red;
}

JavaScript

$(function() {
		$('select').on('change', function(e) {
    		$('#price').text($(this).val());
    });
    
    $('select').change();
});