If you are looking for used, there's a low milage used 2.1L for sale on modularpowerhouse.com. Complete with a 90mm MAF, 75mm TB, cold air kit, and everything else that comes with the kit. The guy wants like 4100+ for it though. Was a little high for me, considering its just a 2.1, you don't get the warranty with it, and he did the install work himself, and wound up with some problems with it.
But i honestly have no idea what used KB's are worth. I saw a 1.7 sell for 3500, so I figured $600+ more was a little much for just upgrading to a 2.1.