to your cost

to (one's) cost

To one's detriment; due to one's personal experience with something negative. Unfortunately, he's not as forgiving as we all had thought, as I found out to my cost.
See also: cost

to your ˈcost

(know, discover, etc. something) because of something unpleasant that has happened to you: Joanne’s not a very reliable person, as I’ve recently discovered to my cost.
See also: cost