You can find used turbo kits on Scionlife or on CStC - just make sure the seller has proof they are in condition and physically inspect them if you can. Personally, unless i can see the physical condition, and check it out from top to bottom - i would not buy a used kit. But thats just me. Others posted on great success with used turbo's.
If you decide to buy a new kit from Dezod,Ptuning or Descendant like im doing, be well prepared to spend over 4-6k for Kit, Gauges, Tune and Install - unless you have a buddy that can help you with the install and DIY.
Dezod's kit is what im going with in the next month - Its a direct bolt up kit with plug and play Engine Management. the MOST IMPORTANT
part of the turbo kit would be finding a competent tuner to tune the EMU- if not, its a good way to detonate an engine very, very quickly.
and keep in mind, if you care about your warranty work on the car, a Turbo WILL void it right out of the gate.
I have done beyond lots and lots of research on turboing as i will be completing my build next month. If you have any questions you can feel free to PM me - im going through the same thing you are.