Personally I love freshwater stingrays. You can get some cheaper $75-$100 which are Florida stingrays, also known as teacup stingrays which do not grow as big. But Motoro stingrays are more beautiful, with great patterns, but will cost hundreds.
Like others have pointed out, Aquabid would be great site for you to check out rares, and prices. If you ever try to keep anything rare, make sure your setup is pristine for the perfect conditions needed for that species of fish.
Great question to see desired fish from all of us.
The worst defeat in the world, is when you give up.