Yes, just type -kindle (starting with a "minus") into the search string.
Is there a way to filter by % off?
That would probably be a bad idea. That list would be filled with a bunch of false "sales" because of how often people(amazon included) put a nonsense List Price up really high and then put their "sale" price down around what that particular item usually goes for so it looks better.
I actually started out having sorting and filtering by % off as one of the core features of so.cool. Then, due to the phenomenon that tielknight described above, I decided to turn that functionality off -- it was misleading more than anything else. Then this is also heppening: https://www.nytimes.com/2016/07/04/business/amazon-is-quietly-eliminating-list-prices.html
Oh okay, that makes sense. Thanks!