I really like Cabela's Hunters TackleBack.
The horizontal slots are a bit small and I have difficulty fitting some of my guns in them. It could be made out of better material but I suppose that's why they are selling them so cheap. AK fits perfectly and can carry extra mags, ammo, handguns, binos, or whatever you want. I would definitely recommend this if you want a cheap alternative to mounting something permanent in your vehicle.