All four of the 2004 GXP window sill trim are faded/corroding.
From looking online I believe its called the "sealing strip"?

Where would be the cheapest place to buy replacement window sill trim?
Cheapest I found was about $100 each($400 total)!

How hard would it be to install?
Would it just be easier to have them painted?

you could always try this
https://www.gmforum.com/exterior-135/window-trim-fix-2000-a-289984/
not too hard to install or remove

Hey Steve, Wayne here how'* things. I checked the thread on repairing the sealing strips. That is awesome since that'* my next project. And to FRANKAR15 I don't believe you can find the strips aftermarket anywhere. Thanks for the info

I hate this about mine too. Look as bad as yours which sucks for the paintjob I have. The "corrosion" aspect makes it rough call to paint. I've been wondering about a black crinkle finish. I really dont want to peel the plastic and make it shiny. Nothing metallic shiny on the car. Don't think it would look good with deep red.

i never got to a write up on doing the upper surrounds on the doors but to do those you pretty much need to gut everything out of your doors to remove those pieces. and John you don't need to go shiney you can use flat or anything ya want however i still highly recommend removing the old vinyl and redoing them from scratch to prevent the issues again. if ya leave the rust on there then it will swell and cause the new top coat to look all screwed up

My driver side looks just that bad also!!! That write up is pretty sweet!!!! Thanks for posting!!

They make a trim low gloss paint exactly like stock. I inadvertently made a thread about this not seeing this one. I used it before on a Grand Am I had and it looked perfect. Paint was Dupli-color DE1634 Low Gloss Black. Need to do the Bonne in the spring. Thanks. BTW, is there any glue that needs to be reapplied to the moulding?

I have an 05 sle with the same trim and it is faded the same way....you could try a product mothers back to black..it gave the trim a much better appearance for mine...and there is actually a GM part number for a silicone treatment for the window seals kinda funny...but I can't recall where I found that at

Back to Black just covers it. I think most of the guys here want to repair.