The Black Rose's cover was at least $20 bucks when I went a couple of years ago, and it may have been closer to $25/$30. And it was cash only when you bought drinks.
My guess is that anywhere known as an Irish bar is taking full advantage of the holiday, and will be charging at least 15/20 bucks to walk in the door. Sometimes, the cover charges start or increase after 9, so you may luck out if you go earlier.