I've been thinking about the same for a long time. There are a lot of pistols available with detachable stocks that do well over 500fps with a single pump.
Powerfull accurate compact, and with basically no restrictions as to car/BOB bag carry.

Inexpensive to boot!

PS, I've got power/water again, after 4 days of Tropical Storm Jeanne.

I had ( & still do somewhere) a pump .177 air pistol by Daisy.
It had decent sights and would bring down birds and squirrels and gofers. Later I bought a rifle like stock for it. Eventually I wore out a rubber gasket in it. Once that was replaced it shot fine. The variable pump was nice, had to shoot mice in my folks living room once. Didn't want any over penetration.