A Tampermonkey script to convert prices from USD to AUD on the Unity Asset Store.

index.js

// ==UserScript==
// @name         Unity Asset Store USD -> AUD
// @namespace    http://tampermonkey.net/
// @version      1.0
// @description  Converts prices on the unity asset store to AUD
// @author       boomboompower
// @license      CC BY
// @match        https://assetstore.unity.com/
// @match        https://assetstore.unity.com/*
// @grant        GM_getValue
// @grant        GM_setValue
// @grant        GM.xmlHttpRequest
// @run-at       document-end
// ==/UserScript==
(async function() {
    'use strict';

    // The interval between checking if prices on the page has changed
    // this only matters if you are doing everything on the same tab.
    // Obviously a lower value means a more frequent price update, but
    // may cause some lower-end PCs to lag.
    const priceChangeCheckInterval = 10000;

    // 1 USD = this much AUD
    //
    // By default it queries a currency conversion API and
    // caches the value for 5 minutes.
    const USDtoAUDExchange = await getExchangeRate();

    async function getExchangeRate() {
        let oops = GM_getValue('dollar_exchange_rate', null);

        if (oops != null) {
            if (oops.includes(':')) {
                let splet = oops.split('\:');

                if (new Date().getTime() - parseFloat(splet[1]) < 1000 * 60 * 5) {
                    console.log('Using cached exchange value. ');

                    return parseFloat(splet[0]);
                }
            }
        }

        let incData = await GM.xmlHttpRequest({
            method: 'GET',
            url:    'https://api.exchangeratesapi.io/latest?base=USD'
        });

        if (!incData || !incData.responseText) {
            return 1.3982793522;
        }

        let value = JSON.parse(incData.responseText);

        if (!value || !value.rates || !value.rates.AUD) {
            return 1.3982793522;
        }

        let audRate = value.rates.AUD;

        GM_setValue('dollar_exchange_rate', audRate + ":" + new Date().getTime());

        console.log('Retrieved a new exchange rate.');

        return audRate;
    }

    function convertAll() {

        // On the main page
        convert(document.getElementsByClassName('mErEH'));

        // On an item page
        if (document.URL.includes('packages')) {
            convert(document.querySelectorAll('._3Yjml > span'));
        }

        // On the cart page
        if (document.URL.includes('cart')) {
            convert(document.querySelectorAll('._3SApE > span'));
            convert(document.querySelectorAll('.tVMIV > span'));
            convert(document.getElementsByClassName('price_label'));
        }

        function convert(arrayIn) {
            for (let i = 0; i < arrayIn.length; i++) {
                let e = arrayIn[i];

                if (e.innerText === e.prevInnerText) continue;

                if (e.innerText.toLowerCase().includes("free")) continue;

                let price = parseFloat(e.innerText.substring(1));
                let converted = (USDtoAUDExchange * price).toFixed(2);

                // I did something wrong :(
                if (price == NaN || converted == NaN) continue;

                e.innerText += " USD\n$" + converted + " AUD";
                e.style.fontSize = "0.8em";

                e.prevInnerText = e.innerText;
            }
        }
    }

    window.addEventListener('load', function() {
        convertAll();

        setInterval(function() { convertAll(); }, priceChangeCheckInterval);
    }, false);
})();