Just an FYI, once this unit has been installed on a FJ (or similar vehicle with this motor), you cannot just take it off. Once the ECU has been flashed for the SC, its staying, unless the vehicle is in a wreck and totaled.
So, finding a used one is going to be very difficult. I have actually never seen a used one for the 4.0L engine for sale in the past 4 years on many different toyota forums.
Try trdparts4u if you want to buy a new one. They have the best prices.
Sometimes a new one is available after the Summit. Someone wins ones but sells it instead to fund other mods. That is how I got mine for a good price. I think 2 became available last year. It is pretty rare though.