Tom,
Here's a site to look at used Cobras. This will give you an idea of the ASKING prices. I took a quick look and counted four ERA's for sale there. ERA builds a top-of-the line product, with a fair degree of exclusivity, as they're only somewhere in the 600's or so at this point.
http://www.cobracountry.com/cobrasforsale-cobras.html
If you provide a link to the car on ebay you'll probably get more responses from people more knowledgeable about ERA's in particular and Cobras in general.
Good luck,
Lowell