This is not a question that WE have to make but appears to be one that is on your mind. The fact is that if, you as a potential buyer, are questioning this home's desirability relative to the proximity to the powerlines, it would be fair to assume that future buyers would as well.
We recommend doing some additional investigation of the possible risks involved with this type of location before making a commitment.
That being said, and to answer your question directly, I'd have to agree with others..if for no other reason, due to perception, I'd think twice before buying there. I'd probably pass. But, as Mack said, this is a personal decision.
Is the home near the stanchion, or do you just see the wires? I had a listing with the stanchion in the backyard. I sat on an open house, and watched cars pull up....slow down....and then quickly drive away, without the people even coming inside to take a look. The home eventually sold (it took a very long time).....for at least 15% below similar homes.....and that was years ago, in a good market.
I am sure it is tempting, and it's a lovely home, as the price should reflect the location. I don't think 10% is enough of a discount, though. This is a big investment..........do your due dilligence, and read up on this before moving forward. There is a lot of information regarding high tension wires on the internet.
Selling a house down the road doesn't need any obstacles that can be avoided right now by buying a different house.
You are likely to find much higher insurance costs.
You should not be surprised if your electrical appliances have much shorter lifespans.
If something happened and the wire broke, imagine it arking and sparking against the house. Could it happen? 20' is not much you know.
Never expect an easy resale if you do buy this. It could be a year or longer to resell, and that in a good market.
Many people believe that those lines will cause cancer, or other ill health effects. Many people see [power lines like that behind a house and just turn around in the driveway never bothering to look at the house.
Those people may be wrong, maybe there is no real danger to people from those lines. BUT as long as that perception remains your buying pool will be very small and slow arriving at your door.
For the best deal look at a house without known objections. You do not want to buy a house you could never sell. A freeway in the backyard, a toxic waste dump nearby, a cell phone tower, big windmills, and yes, those ugly power lines all effect the desirability of a property.
The fewer objections you buy into the less problems you will inherit from the place you purchase.
But I once did a few open houses for a friend at one of their properties which had one in the backyard and every single person loved the house and when they saw that, they were not interested. So although you may not mind, think also about resale.