I ordered my remanufactured ABS Brake Booster Pump Motor off ebay.
2003 2004 2005 TOYOTA 4RUNNER LEXUS GX470 ABS Brake booster Pump motor (REMAN)
It was $375 when I purchased it. You'll get $100 back for the core exchange. It comes with a 2 year warranty.
I bench tested the motor by itself when I received it. All good.
I removed the entire Hydraulic Brake Booster assembly using the numerous online videos, but this one helped the most especially since it was for a 2004 4Runner...
How to remove the HBB ABS unit from Toyota 4runner , Lexus lx450 lx470 gx470 etc
I kept the HBB unit upright during the removal, the motor replacement and the subsequent re-installation. I have no idea if this is important, but I wanted to make sure as little air as possible got into it or any of the brake lines.
This video was the most useful for replacing the motor on the HBB assembly.
HBB new motor install 4runner gx470 lx470 abs unit screeching screaming noise
It was a small PITA to do keeping the HBB assembly upright, but that's how I did it.
I then bench tested it by using the power connector on the bottom of the ABS Modulator. All good.
I re-installed the HBB assembly. I haven't bled anything yet. The piercing buzzer is gone and most of the dash warning lights went out. The only 2 lights still on are VSC TRAC and TRAC OFF. I'm gonna worry about them another day. The brakes are working just fine, not as tight as they can be, but well. I'll get them bled eventually.