If it will be a Centerfire on your belt, I say go with a small light 9mm to keep plinking costs down & be good for defense. There are many to choose from. And just a sampling, in the last few weeks I bought two different 9mom's that were barely used that were both well under $200. A Canik TP9 SA (like a Walther 99) and a Tristar imported Canik C100 (like a CZ 75 compact).
If you mean to keep it in your tacklebox (which means no self defense to me) then a stainless .22 auto (Ruger comes to mind) or even a stainless or plated revolver. Ruger .22's can be bought cheap once the finish starts to show wear. And they keep going. Again, a small 9mm won't really take up any extra room.
Another thought is to find a CZ 52 in 7.72x25. They are tough reliable ex-military guns, were always inexpensive (dont know about these days) and the round is cheap to shoot and Hot. I paid $125 for the one I bought years ago, like new with holster and spare mag. They are probably double that now. Loud though...
