If you haven't already, contact Abby at Flightline. She can send you out swatches of all the available fabrics, as well as prices for custom options.
Personally, I didn't like the faux leather standard material, and I also heard that it might react with the interior (rattle can) paint I used, so I decided to use Marathon fabric (black and red) for everything. Marathon is the woven fabric that is in the center panels of the standard seats.
I'm really happy with how everything turned out. It's not as plush as some of the more expensive options, but I think it gives a sportier look and suits the -12 nicely.