They are now listed as unavailable on Amazon in the US. When I looked, the lenses were only about 8 Euros in Europe, so presumably the $250 was some scalliwag attempting to cash in on the Google Cardboard hype.

Could be pricing algorithms gone wild, too. For a really extreme example of this, see: http://www.michaeleisen.org/blog/?p=358

There's a website called Surplus Shed that someone else linked. I found 25mm diameter, 40mm focal length double convex lenses for $4.50 each. You can put those parameters into the finder yourself here: http://www.surplusshed.com/lens.cfm