98 Mercury Sable 55,000 miles

I am afraid I know the answer, but today on my way home from work my temp gauge was right in the middle where is should be, after a bit I heard a tick sound coming from under the hood, I was only a few miles from home and other than the tick it was running okay and wasnt showing hot, I have a small leak in the radiator so figured I was low on water, anyway, my car died. I pulled over and went to start it back up, it started but I was afraid to do any more damage so I shut it off, after a bit we took the radiator cap and were shot with nice pretty rusty water, and then looking in the radiator there really wasnt any more water in there. (The amount that came out was small) the next time I went to try to start the car it turns over but will not fire. WE had the care towed home, and the tow truck driver just shook is head and said, its done. And figured the timing belt? May have broke or jumped? But why would it start that once? What is the usual cost of having that repaired? And what are the chances of it being anything worse?
Obviously I drive a 98 Mercury I have no money, and only the one car. I'm desperate.