How much? Depends on the Name.. Keep in mind that any name brand you buy .You can still use the K&N filter..(thats the most important part..) I personally have a homemade one that didnt cost me anything other than the purchase of the filter..(Thats a little steep but well worth it..)
Easy to install?
Even if you buy the Fipk. It is very easy to install..
Yes they do.. Moderately ..BUt its a big performance boost..
I only gained about 1 mile per gallon. But I bet I gained at least 10 or so horsepower.. Incredible considering it was a piece of electrical conduit( 2 1/2" ) and a K&N filter No problem.
By the way the entire FIpk Kit is about $250 .
I could tell you how to make it for much less.. But you wont have a splash shield.. (Unless you cut your factory box.)
I think the 2 1/2" conduit about 2feet long with a 35% bend
would have been $3.50 or so.. Up to you.. There are lots of ways to do it..
God I ramble...........