Could my serpentine belt be the cause of my car stalling?

I have a manual 2004 Ford Focus. It's got around 123,000 miles. Over a month ago I had some work done and I told my mechanic about the squealing noise I had been hearing the last few weeks. He had mentioned the serpentine belt needed to be replaced as well as the timing belt. Also the valve cover gasket. He said it was best to do it all at once as far as labor cost goes. He quoted me almost $600 to do everything. Well, I told him I would have to save up for it and went on my way.
Just today I was driving and stopped to drop my son off somewhere. The car drove perfectly fine. But 5 minutes later when I returned back to the car and started it up it stalled immediately. I kept starting it up but it kept stalling. I finally managed to back out of the driveway, peeling out as I drove away so my car wouldn't stall again! The whole drive home the car kept stalling every time I let off the gas pedal to shift to neutral, brake or turn. But I finally got home and am staying until I know it's ok to drive it somewhere to get it fixed.
I'm trying to figure out if it was the belt finally breaking (even though I didn't hear or notice anything prior to this incident)that may causing my car to do this or if it's just one more problem and expense to add to the list of stuff that I have to do to this car? Anyone have some idea or advice (other than trade in this piece of crap before the engine blows). Thanks for your time! -Gina-