you can probably break even selling the 18s you got. as someone who has 4 set of rims for a prius and 3 sets for the z, i know how you feel about rims and tires
www.tires.com has better pricing than tirerack, get the konigs mounted with kumho xs, it will be cheaper. xs is roughly the same as the re11 at the track, but they are noisier and they are slower in the rain. i went with re11 as 285 35 19 is cheaper with the bridgestone. 275 35 18 is a different story.
i will sell you my 5zigens with race rubber for $950 hehe