Calculate money on page https://store.steampowered.com/account/ . It is jQuery variant this gist: https://gist.github.com/Sintetic/6797297)

getMySteamPrices.js

var summ = {
	store: {},
	gifts: {},
	market: {
		sell: {},
		purchased: {}
	}
};

var selector = '.transactions .transactionRow, .hidden_transactions .transactionRow';
//get transaction blocks items
var transactions = {
	store: jQuery('#store_transactions div.block').first().find(selector),
	gifts: jQuery('#store_transactions div.block').last().find(selector),
	market: jQuery('#market_transactions').find(selector)
}
//get only number from price (for example: "0.10" from "$0.10" and "24.04" from "24,04 руб.")
function getPrice(str) {
	var rez = '';
	for(i=0;i<str.length;i++) {
		if (!isNaN(str[i])) { //if numeric
			rez = rez.concat(str[i]);
		} else if (str[i] === '.') { //if there is a separator
			if (!isNaN(str[i-1])) { //if the number before the separator
				rez = rez.concat('.');
			}
		}
	}
	return rez.replace(' ',''); //removing any spaces
}
function addPrice(item, rate, keyPlace) {
	//get item price with currency
	var line = jQuery(item).children('.transactionRowPrice').html().replace(',','.');
	//get item price (number only)
	var price = parseFloat(getPrice(line));
	//universal get currency in this item (it's magic!)
	var currency = line.replace(getPrice(line),'').replace(/[\d.]/,''); 
	if (keyPlace === 'market') {
		if (!isNaN(price)) { //if price is number
			if (typeof(summ[keyPlace][rate][currency]) !== 'undefined') {
				summ[keyPlace][rate][currency]+= price;
			} else {
				summ[keyPlace][rate][currency] = price;
			}
		}
	} else {
		if (!isNaN(price)) { //if price is number
			if (typeof(summ[keyPlace][currency]) !== 'undefined') {
				summ[keyPlace][currency]+= price;
			} else {
				summ[keyPlace][currency] = price;
			}
		}
	}
}

jQuery.each(transactions, function(keyPlace, place) { //actions in each transaction
	jQuery.each(place,function(keyItem, item) { //actions in each item transaction
		if (jQuery(item).children('.transactionRowEvent').is('.charge')) { //for all
			addPrice(item,'purchased',keyPlace);
		}
		if (jQuery(item).children('.transactionRowEvent').is('.walletcredit')) { //only for market
			if (keyPlace === 'market') {
				addPrice(item,'sell',keyPlace);
			}
		}
	});
});
console.log('Store: ',summ.store);
console.log('Gifts: ',summ.gifts);
console.log('Market:');
console.log('  Sell:      ',summ.market.sell);
console.log('  Purchased: ',summ.market.purchased);