I purchased from Lseat.com for under $300, and installed by a local shop for $250.
After reading some of the comments on previous threads about this subject, I realized that proper installation was key to making the seats look good. So I decided against DIU in favor of a pro installer I found on yelp. Here's the secret: I asked the installer to add additional foam because after 15 years, the original foam padding isn't as good as new.
I am
very happy with the result. As good as OEM? I know that some Porsche purists would never be happy with anything less than OEM, but my seats are much better than it was last week. This must be as good as you can get for $550 total.
Sounds funny, but I'm much happier driving the car now, and not embarrassed about even valets noticing cracks and rips in my old seat leather. I think I'll keep the car for another 15 years, now!
BTW I switched from Savannah Beige to Black leather and I like it much better.
edit: Been a couple of weeks now, and I'm still very happy. I love the "new car smell" of the leather. My Boxster smells like a new baseball mitt.