Why did my car shut down??

It could be the main relay or the fuel pump.
Have the fuel pressure and relay checked and let me knwo how it goes.

said it was timing belt. said i would have to change water pump too. gave me a quote of 450. does that sound right?

Well, if the timing belt completely failed, there may be severe engine damage that might require a rebuild.
Before you have the work down, have a cylinder compression and leakdown test performed on all cylinders. This will ensure that the valves did not hit the pistons and you won't be getting into a money pit.
The water pump is easy to replace whne doing the timing belt and I would reccomend that along with a timing belt kit. A kit includes a new trensoner and idler pulley as well as some other parts and all the accesories belts. This should not change the labor at all.

As far as the estimate, it seems fair, I did it with the 4 cylinder engine. It came to $422.86.

Parts $110.86
labor hours 6 hr@ $52/hr
rate $312.00

I hope this helps you out.
Take care.