Brake pedal goes to floor - please help

My 2009 X3 has a brake pedal going to floor.
-last week had to super pound brakes in traffic. Bit
later brake light went on. Checked fluid and some
was lost. Topped off and all was fine. DOT 4 as
specified.
-Two day later light back on. Topped off again and
all was good. Got up next morning to wet spot at
drivers side rear tire.
-Topped off again. Need car to hang on until
Monday which is payday to get to garage.
-Tonight brake light went on. Topped off again and
all was well. About an hour later the pedal went
straight to floor. Pulled over and checked master.
Still full and no fluid gone. Tried resetting system.
No help. Pumped brake a ton and pedal came up,
but only for a few seconds and back to the floor. No
fluid missing. I need to use this car tomorrow and
the next day for work. With the weekend most
shops are closed. I need a miracle! Hoping you
folks might be able to provide the miracle I need for
two days. Thank you in advance for any help or
suggestions. Needs to be cheap!