JSFiddle - React, Tailwind, and code Playground

HTML

<script src="https://code.jquery.com/jquery-2.2.4.min.js"></script>
<input id="myTextField" type="text" value="50"/>

JavaScript

var price = 50;
var value = $("#myTextField").val(); //e.g value = "+50"
var finalprice = price + parseInt(value, 10);

alert(finalprice);