Water pump problems

Hey guys. I recently bought a used '93 Jetta GLS from a friend of a friend. The car however seems to have needed a lot of TLC because I've had to put a lot of money into it to get it back to shape. It needed a new alternator, heater core, the fan wasn't working properly, and a new water pump because it was leaking coolant. After having this "friend of a friend" (who by the way is a mechanic) replace the water pump, it seems again that the water pump is leaking again. I have not had it diagnosed professionally, but it's visually obvious that the leak is coming from somewhere along the timing belt near one of the pulleys. I know the water pump is located there so I'm thinkin that's the problem. My question is, can a water pump fail so soon after replacing it (approx 1 month)? Or could it be that another more serious problem is causing the water pump to fail? Also, I wanted to know can the water pump cause the head gasket to blow? If my water pump is leaking coolant, but i've been replacing the coolant frequently (3 times a day, enough to keep the car within operating temperature) is there any way to blow the head gasket?

Sorry, 1 last question. I want to send my car out to a volkswagen dealership to have it serviced by Volkswagen mechanics who know what they're doing. The car is now leaking coolant as well from the reservoir. I wanted to get them to replace the water pump, have the timing belts changed and tightened, and have them replace the coolant reservoir tank and hose. How much labor might be involved in this job, and how much do you think is a reasonable price to pay for just the parts alone?