AccordCoup94

ok.. my car is fuked.. im driving normal.. and all the sudden, i hear this chain dragging sound from my rear. i think it was my rear brakes locking up. and when i brake, i have to step all the way down to stop the car.. and even then.. it takes a long distance to complete the stop. now.. i just got home and i put the car in reverse to back up into my space, and my brakes lock up. WTF! so i force the car to move, even though the brakes are locked on without me doing it and i get into my space. whats my problem??? im thinking its my master cylinder, but i have no clue. if it is, how much does it cost to replace it and can i do it myself? if anyone knows, some instructions would be greatly appreciated! maybe i can pick up the part at pepboys. thanks to anyone that can help me. i know its dangerous to drive the car now.. im scared.