Lumia 521 has been real difficult to grab at the price of $129 from retailers because of quickly selling out after coming in stock. Currently, it is in stock at Bestbuy, which has always priced it at $129, but never had it in stock after selling out the first stock.
Also at Amazon, it is now again priced at $129 and in stock now. Bestbuy quotes 1 business day for shipment, while Amazon says that processing may take 1-2 business day.
In case, you want to know more about Lumia 521, visit our lumia 521 page for features, specs and deals.