The Redragon Impact M908 has its own numpad on the side (with 12 buttons) and it's under 40 bucks. You could game with just the mouse (no KB ) if you had that. I tried it out once to see what it was like, and it was cool to bring up menus without having to move the mouse somewhere to click.
I'm a bit conflicted. One the one hand, it's quite visually cool to make bodies of water that the player can interact with by going into it. However obscuring the player character from a gameplay perspective is pretty bad. Hmm... There's the option to make the area around the player visible, but then that kind of defeats the purpose of submerging them.