I have an SKS with a Dragunov stock and 40 round mag that would work for me. Now if I had the $800 I would look for a used AR-15 or an HK91, .223 and .308 are fairly easy to come by.
It's kind of funny, I was hiking with 3 friends last year and one of them asked, "What would you do if zombies attacked like in Dawn of the Dead?". The funny part was not our answers the funny part was we all had an answer to begin with. Thinking about being in a survival situation where you get to shoot enemies that are already dead is kind of fun.