Soooo i've had some very bad news, my master cylinder is apparently stuffed and is leaking brake fluid all over my engine bay

I took it in to the mechanics to get my new brake pads/ discs machined, asked them to check the leak, got it back the next day with the all clear after the last of my savings was handed over. 2 days later and my brake fluid warning light comes back on ..WHAT!?... sure enough i've lost half my fluid in 2days!!
sooo back to the mechanic, he now tells me i need a new master cylinder argh! i was very angry that it never occurred to them to check it the first time i brought it in, especially since i made a point of asking them to check it and i would have just got that fixed instead of getting my discs machined, so the money is gone and what do i do?---i keep topping up that damn fluid and watching it leak all over my garage floor:(... soooo i've completely lost faith in my mechanic and will not be returning to his "fine" establishment.
Anyways so the point of this thread is anyone willing to help me fix it with guidance or has a reconditioned master cylinder that their willing to part with, i will be more than happy to compensate, you'll be saving a poor uni student some undue stress

cheers