I have red dot that I took off my MKII when I bought it. It's cheap one. Pretty cool, but I'm trying to get better with iron sights. It's a BSA. I think they are like .....$35.
Just as another data point, I've been happy with a FM Optics (I think it's called) red dot sight which I picked up from the good folks at Bradis. The price was well under a hundred bucks (that's all I could afford at the time).
I've been using that sight on a rimfire pistol -- frequently -- for just about two years now, with only an occasional hiccup. The FM optic has never drifted off zero; and I use it, successfully, for target work out to a hundred yards. But anymore, it sounds like the TR-25 is a good way to go, too, for under a hundred bucks.