Oleander grows 15-20 feet tall and is salt tolerant. It is more like a huge shrub than a tree, but that may actually be better as it will provide privacy from the ground up.

Carol in Jacksonville

Here is a link that might be useful: Google Images - Oleander

Another good option is Pittosporum, which is technically a shrub but which grows to the size you want in my sand on an island near Wilmington. It needs no attention whatsoever, and is evergreen.