$80 plus postage is about right for most cars

You don't have to replace them just clean and oil them instead; sounds easy? It will probably take you all day the first time as you have to let it fully dry before oiling and you will probably over oil it the first time which means you have to start over again :P

I have K&N in all my cars; so they must be good :P

As for performance and economy they are better flowing than most paper filters so you might see increased performance; you might not