If finances dictate a common caliber, I would suggest a .357/.38 pistol and lever action carbine. Good stopping power, relatively inexpensive and ammo is still pretty common and available. I’m not sure of the ballistic numbers, but I suspect it will give you good distance. What kind of distance are they looking to reach out and touch someone?
Another option, might be a common rifle caliber, and a common pistol caliber, such as 7.62X39 for carbine an 9mm for pistol.