New water pumps aren't super pricey and a good option if it's also about time for a timing belt (100k). However, I assume the car needs to run right now. I would say just toss the new one on and drive the car. I too find it very odd that a thermostat could break like that. Like was said, it was more likely cut. As was said already, you can certainly inspect the water pump too if you feel like taking off the timing belt (not really hard to do). The only problem you may have is that the old timing belt may have its timing marks worn off, so you may need to remark locations again before removing.