I go as cheap as possible for cabin air filters, but I don't skimp on engine air filters. K & N would be my last pick for an engine air filter however. Watch the Project Farm engine air filter test. The K & N performed poorly by a wide margin.
Project Farm's engine air filter test (skip to the bar graphs at the end if you don't want to watch it all) -
https://www.youtube.com/watch?v=sJ3L-E-ufYo
I tend to buy the Wix from rockauto.com, but there are others that are good, too.