Here are some nice megillah cases that come made to order in various sizes all the way up to 25 inches. The tube is wrapped in a polished leather with a nice sheen. The top and bottom are made of hard wood. Please call for a price on any of these cases. Measure your megillah before you call so I can provide an exact price.
This megillah case is designed for a large 20 inch megillah. This style and size is $175.
Here is a closeup so you can see the details.
If your megillah has an eitz chaim this case would be a good choice because they can hold a megillah up to 25 inches. You can also or an eitz chaim for a megillah ($130).