1995 Volkswagen Jetta Water Pump

For the past month I have been having to replace the coolant every week or so, then it went down to every 3 days and now for the past few days every hour. At firs t I couldn't see where the leak was, but finally found it in the very front of the car where the radiator is. I took it into a mechanic and he told me I needed a new radiator which would run $326. Now a day later he calls me to tell me I need a new water pump because it is just gurgling. The cost is an extra $420. If I don't change it, a head gasket will blow. Should he have been able to determine that the water pump was bad before making a decsion about a radiator being bad? Do you think I need to replace the whole radiator or am I being taking advantage of?