Why not a Handi-Rifle?
Inexpensive...
Chambered in everything from .17HMR to .308 to .45-70...
Innocent looking (esp. if broken down in a nylon duffle bag or lockable briefcase)...
Accurate...
Quick to action (with practice, you can fire, reload from a butt-cuff, & fire again as quick as operating a bolt-action repeater)...
On a recent camping trip, I took along my Stoeger Coach Gun broken down into a lockable briefcase. I found that, starting from the locked case, I could have the shotgun assembled, loaded, and on target in less than four seconds. And I bet more practice could get me faster. (I also had a pistol loaded & handy, just in case I didn't have four seconds...)
Just another thought...