[JLStock]

I have a R title 428i XDrive with 23k miles. Temp @5am was about 7 deg. F.
I back out in driveway, stop and head up long driveway, light brake a bit, turn on road, drive 1 block, light brake, turn on road. I forgot lunch so I decide to turn around. Drove less than 5 to 7 min. I try to stop and I think it started to brake, then nothing. I think I used my E brake to stop. I release E brake and have foot on brake pedal and I start to move forward. I believe the ABS light came on at that point. I run car around, drive down hill on my driveway and into to my garage using brake pedal to stop. Shut car off and locked it as I go in house.
I then drove to and from work with hand on E brake. Brakes seemed to work both ways.
Any idea what would cause a complete brake failure? Is there a sensor or motor or do I just likely need a brake fluid flush? Any idea what the cost is?