What I'm guessing is that they're just not as complete as other turbo kits. I'm not sure what every turbo kit comes with, but I specifically remember reading about one (Incon twin turbo kit I think) that came with a specially calibrated computer, larger MAF, and larger injectors. Just those items alone would probably equal close to another $1K, not to mention all the little items I'm not thinking about right now.
It comes with two Garrett turbos so it can't be all that bad, but then again it doesn't specify whether they are new or not. After a quick search online I found two places selling the Garrett GT28RS turbo for $1,150-$1,175 EACH. So the question is whether the ones in that kit are used/rebuilt or places above are highly overpricing them.
If you go for it, let us know what they're like.