1998 Buick Regal Steering problems

Hi I have a 1998 Buick Regal. Lately my steering wheel has been tough to turn. When I first start my car it runs fine. Then about 20 mins into my drive my steering wheel becomes very difficult to turn (almost impossible). At first I thought it was my power steering pump but after a trip to the local mechanic I found out that it is not the problem. I then took it to a second mechanic and was told that I had to replace my rack and pinion. They replace my rack and pinion with a after market one. Later that day the same problem occurred once again. I then asked for my money back. I just took my car to a third mechanic and they told me I have to use a stock Buick rack and pinion (no after market parts). They let me know the price at which it would take to fix it and it is more than what I paid for the car. Please help me solve this problem. Are there any other solutions?