Will not start

This engine very rarely survives a broken timing belt. It is an interference engine so the second the belt brakes, the pistons hit the valves and bend them. A leak down test with answer that, but you are likely looking at a new engine if that is the case.

Not with 194,000 miles on it. The lower end is too far worn out and would not handle the pressure of the top end being rebuilt. A used engine would be your smartest move once you confirm the valve problem.

Unfortunately it does not work that way. First of all there may be piston damage from the impact. The valve seats and valve guides are going to have a lot of wear so a new valve just is not going to mate up to the head without a lot of machine work first. You cannot machine only some cylinders. There just is not any way to do a patch job.