Occasionally, you can find used ones at eBay for $150 to $175
When I lost my first reader, I bought a replacement on eBay for $150. I had to call Sony to reset the owner information, but that was the only inconvenience. It's worked without any problems for about a year.
http://cgi.ebay.com/Sony-PRS-500-Ebo...QQcmdZViewItem