Supply and demand. There weren't many to begin with, and while demand may have cooled, so has the supply since only so many Silvias were produced in Japan.
Plus, the market stabilized at that price. Vendors are less likely to alter prices unless they feel they need to for the sake of moving product.
But yes, that's an average price for a Silvia front, unless you watch eBay like a hawk, you'll have difficulty finding a better price.
The only price I can find that's slightly better is $800 from JGY
http://www.jgycustoms.com/240sx/exterior.htm