Magnetic fields are misunderstood, and seem scary to the public. This fear makes potential buyers, such as yourself, reluctant to purchase a home near a power line. When you are ready to sell, you will face this same problem. Thus, powerline proximity does depress property values.
The studies to date show no link between power lines and disease. Check out this summary.
I also wonder why you’d want to buy now. You’ve heard of the “greatest fool” phrase, right? Anyone buying now is that greater fool. I don’t mean to insult. If you have money to burn, get a sports car. You’ll still enjoy it and won’t kick yourself when prices come down.