A dual 1581 drive on eBay (http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=280115849825) starting at $50 and FREE Shipping (US Only). This guy's mod is not quite a 1582 according to his description -- just two drives in one case -- so won't support drive 0 and 1 or the best thing of dual drives the Backup command.
It'll be interesting to see how much it sells for.