That's a lot of calories.
Recently, the husband of Lindsay Smith, one of the gals who placed really high in the 09 Games posted they spend $1500/month for the two of them and one child (which I want to say is 1-3yo).
What I spend right now isn't worth commenting as it's neither Paleo/Primal or Zone. I'm happy if there is food in the fridge but it heavily consists of milk, eggs, hamburger and some fruits and veggies, maybe some cheese. Right now there is literally 2 strips of bacon, a nearly full gallon of milk, and a dozen or two dozen eggs. Some green stuff and that's about it. Some of my food budget tends to be stuff for lunch on the way to work or close to work since if I have to go back home to eat, it's unlikely I'm gonna go back to the gym to workout though I might end up working out at home.
I'd have to crunch numbers but 600$/month sounds about reasonable for that many Kcals&Paleo. It probably depends on the amount of meat you eat and what kind.