I have looked into changing the rear tail lights to the 98-00, but each side is roughly $200. Not worth it, unless they somehow get damaged. THen I would do it.
As for the headlight lens, I believe those are a little cheaper. Something like $125 (don't quote me). I think you can get the 98-00 ones at bekker.com. I have also thought about doing this. But probably will not until/if it needs to be done.
As for the HID, you're looking at $1700 + to get OEM ones, DEFINITLY not worth it.
The turn signals (clear corners) can be had for a lot cheaper (I think about $50 or so). You can try www.bekkers.com
for them, I think they have them There was also a recent post in the OPEN DISCUSSION on this (probably on 2nd page now). Try looking there.