There aren't that many hosted singles cruises. I would suggest you open your departure from another port or open the dates of departure to find something. Also they tend to be more than regular cruises so finding one in that price range is even harder.
Why not just book a regular cruise, every trip has singles on it you just have to ask around at the bars for who is single. Most will have one singles event where you can meet other people, if not you just have to ask and they will add one