1994 Ford Explorer Fluid leaking under front tire on driver

Brakes problem
1994 Ford Explorer 6 cyl Front Wheel Drive Automatic

I was on the way to school this morning and the brakes was going all the way to the floor. I noticed that the brake light came on when I parked. So, when it was time for me to go home. I noticed that there was a big wet shot under the truck. I took my time driving home. I looked under the truck and noticed that the front tire on the driver side was wet. I touched the wet spot and noticed that it was oily. I assume it was brake fluid. What could have happened? And, What am I looking at in cost wise?