My bro had a XK 120 way back when. He bought it for a song. Never got to drive it much because it always had an electrical problem somewhere. I drove that car fast a few times and I will never forget that experience. A few things to know. They burn a lot of oil, the sump holds 9 quarts and they leak. Carbs are hard to tune.
I don't think the price of the car would be my primary consideration if I wanted one. I would have to locate a good Jag mechanic and have them evaluate it. Then ask them what they would charge to keep it tuned up. It won't be cheap. Oh, and parts. Never mind.