Here are a few places

http://www.performance-air-filters.c...filters-2.html

I got mine at ($65.50 shipped for the E2427 - direct drop in)
http://www.performanceintl.com/

http://www.martelbros.com/cgi-bin/st...ore=direct.KNN

$65-$70 including shipping is good for the E2427
and $35-$40 shipped is good for the RU2820