On my Ford Focus Wagon ZXW SES (2005), my mechanics say the air filter housing and filter must be replaced as a unit. Their 'life expectancy" is 100k miles. I'm told it is a $300+ part/replacement cost. Can anyone verify this for me?

i would check with dealer parts to verify if you doubt your mechanic. i wouldn't go there if they can't be trusted.

This is true for the 2007 Focus and it sales for a little over $330.

The 2003 with the 2.3 liter engine is the same.

In '05 - '07 the 2.0L and the 2.3L have this expensive filter as well.

Accroding my info in '08 things went back to normal.
https://www.midtennfordparts.com/focus-parts.html

this is what alldata has for pricing, may be it's wrong?

Part OEM Part Price
Air Filter Element
Air Filter
Without PZEV 8S4Z9601A $49.36
With PZEV

Part Of Air Cleaner Assembly.

Labor Skill
Level Mfg.
Warranty Standard
Air Filter Element
Replace C 0.2 0.3

Thank you for verifying. I did check with the dealer and got the same answer. I totally trust my mechanic, just could not believe this ridiculously expensive component! Has anyone ever taken one apart and looked at the insides to see why it is so darn expensive, and if all contained parts require replacing? Maybe that is more trouble than it is worth....