script.js

// ==UserScript==
// @name         New Userscript
// @namespace    http://tampermonkey.net/
// @version      2024-12-20
// @description  try to take over the world!
// @author       You
// @match        *://www.preciosadictos.com/*
// @icon         https://www.google.com/s2/favicons?sz=64&domain=preciosadictos.com
// @grant        none
// ==/UserScript==

(function() {
for (const e of document.getElementsByClassName('prco')) {
	let n = parseFloat(e.getHTML().replace(",", "."));
	e.parentElement.append("Cliente: " +(n * 1.21 + 50))
}
    // Your code here...
})();