Brake pedal goes to floor

[SJ]

90 100q
Wife wanted to take the car out. Put foot on brake pedal . . it goes down to
floor.
No apparent warning . .no soft pedal, etc

I suspect the master cylinder is shot. I find no leaks anywhere. Will jack
up the car tomorrow and check more closely.

Does the master cylinder fail is such a sudden way?
My parts guy says a new one is about $150. No rebuild kits for this.
P/N is 893 611 021 . . both brake lines are on Port side . . bleeder valve
on end.

Is that price about right?

SJ
85 Dodge PU, D-250, 318, auto
85 Audi 4k - - sold but still on the road
88 Audi 5kq
90 Audi 100q