cheap hootch will hurt you more than higher dollar stuff. And you hit it right on the head assuming it is impurities.
There is a reason some liquor costs more than others.
As for Blends like 7 Crown or Kessler, it doesn't much matter. Go cheap, all the blended whiskeys have a substantial amount of neutral grain spirit (vodka) in them.
Canadian whiskey's like Crown Royal, Canadian Mist, Canadian Deluxe are all pretty similar in taste. They are all blended and a little sweeter but should not have vodka cut into them. You pay more for the hangover factor.
Again impurities. I like Canadian whiskey personally.
We sell a label of lower dollar bourbon. It is cost effective and tastes okay, but I ain't drinking it nor will I name it here, LOL