I have a Naga Razer mouse, the one with 1-12 on the side which is built for MMOs, and I love it. It takes some getting used to, but once you've got it figured out it works a million times better than using the numbers up top on the keyboard. One thing I did in-game to help with adjusting to it is arrange my hotbar so that it mimics the layout on the mouse. The numbers are four rows of 3 numbers going horizontally, so 123, then 456, then 789, then 10, 11, 12. So I arranged my hotbar to look the same way, and function the same way. It took some messing with the game's default keybind, but for me having the hotbar on screen and the buttons on my mouse visually match up is very helpful. But this was in Final Fantasy XIV, so I'm not certain that WoW or DayZ have such flexibility. Either way, I know people who haven't done this to their hotbar and use it just fine.
I got mine used on Amazon for $60, but as with anything like that it just sort of depends on what's available.