Why do you think you need one???
Do your brakes work???
If your hydraulic pump (actuator or whatever) is bad, you can't wait till later if you want to drive the car because you don't have any brakes without it. At least not enough brakes to be safe.
What symptoms are you experiencing that makes you "think" you need a new system? I'm not sure I would make this investment based on some codes that a mechanic pulled from the ABS controller.
If it is bad, go to Prior and get a Teves Mark II ABS unit. If you ordered the accumulator from them, they will cut a deal on the unit without the accumulator. Just swap the one you recently installed onto the new system.