Brake trouble, and its causing me a lot of it.

Hyundai Elentra 2000

My question today is hopefully an easy one.
I recently had my back brake pads replaced. The person who changed them had trouble bleeding the driver side brake, However I did have brake at that time. Slowly, through out the time that I had it fixed the brake peddle would pump then go right to the floor at a stop. *Signs of the master cylinder*
I took the car into an auto repair shop and he informed me that the problem was not with the bleeding of the back brakes it was the master cylinder. $310.00 later, 185.00 for the cylinder and $110.00 labor. He now informs me that there is another problem. The Proportioning Valve is not working and he cannot blow it out. “ I was instructed to drive it” that I would only get front brakes from time to time. The valve will either blow it self out or we will need to replace it. I drove the car one day, felt a bit of play during the day, then all of a sudden no brakes. Pumping does not work at all now. Brakes go all the way to the floor but I can get a stop in… Full stop, peddle is to the floor. Now I have been looking on the web for Proportioning Valve” some type of information about this. I am not finding “ how to’s” anywhere for a Hyundai Elentra. The Mechanic is telling me that this valve is going to cost 185.00 for this part. I am wondering if I am getting hosed here. “ No pun intended”. Can someone help me? I am worried about taking it back and not knowing anything. I do need to call him and tell him that I have no brakes. Also if it is the proportioning valve would it act like the master cylinder is out again?”