For a completed unit ready to bolt in around 1.5k for the most basic
If you buy an aftermarket unit ala OS Giken or quaife/wavetrack you still need to pay somebody to install it. Costs of those completed are 2.2-3.1k; machine work still required.
OS is the best but cost is quite a lot more when all done.
Completed units will be done in a few weeks, cars are already slotted for them