A gun that would work well would be the 7.62x39.
Ruger's Ranch Rifle is available in that caliber, or you could just get an SKS, they are very cheap. My dad bought one for $80 back in the 80's before the assult rifle ban, and the gun works as good as ever. Nowadays you should be able to get one for little over $100. The 7.62x39 is only good for shots within 100 yards, in my opinion, but within that range it'll do the job.
It doesn't kick too hard, and it's semi-automatic, soif you want to, you can make follow up shots.