Cruising Catamarans Offshore
Lifting keel boats are more expensive than fixed keel boats and $50k is not much for an ocean going boat.
The less expensive lifting keel that I know is the Feeling. It is made by Kirie and even if the 36 (new for around 150k euros) is a Class A boat (European Classified as Ocean going) I would not call him an ocean going yacht.
Regarding cats, I find this sailnet article fair and interesting: