I personally do not have any experience in shift kits, but you can et one from (for example) LRS for $80. This is their description:
Like I said, I have experience with nor have I heard any reviews on them. However, what I do know is that tune would not only do everything a shift kit does, but it adds power too. The only way to get a tune is to buy a tuner. American Muscle.com sells the SCT tuner with free tunes for life from BAMA Performance. Along with having added performance from their tune, they turned my auto into an animal. Shifts hard and at the right RPM.