Other than the AA12 the KSG shotgun might be the best “zombie gun” out there. I am told the MSRP for these is in the $700-800 range but because Keltec limits the quantities manufactured and employees get dibs on them the actual price available to the rest of us is with a 75-100% markup (employees buy and then resell). But I am hearing that Keltec is giong to increase their manufacturing, one can hope. I would probably buy one for about $750.
Here is a review posted on youtube but there are better videos that shows it true capabilities, I recommend checking them out.