I have what is essentially a gun locker. It's mfd. by a gunsafe maker but an angry look would get you in--before I modified it. It's about the size of a grey military wall-locker with the feet removed and has a keyed lock in the handle which, when turned, pins the door top and bottom. It weighs about sixty pounds and cost about $100.
I went to the local hardware store and bought two 4" hasp and staples and a couple of those round Master locks for about $40. I mounted the hardware top and bottom on the door, double nutted the bolts then bent them.
I was able to find one stud (where I had room for the unit) and put a 4" lag bolt through the middle of the back of the cabinet, top and bottom, then flanked each bolt with 1" toggle bolts. I put 1 1/2" washers on each bolt in the back, so a quick jerk won't pop the bolt-heads through. 2 1/2" lag bolts with 1 1/2" washers in each corner and the center of the floor completed the installation.
This installation is in the spare room, upstairs (that's why I don't have a 600# safe). I seldom lock everything up unless we're going out of town--when those Master locks are engaged, the hasps fit so tightly over their staples that the key will barely turn in the lock. It usually takes me two or three tries to unlock it. When I leave, I hide it with cardblard--actually, the box it originally came in, split open along the seams--then pile junk in front of it.
I realize that this arrangement will not deter anyone who's after the guns and has the time, especially if he realizes that I keep my power tools in a locking closet on the back of our unit (we live in a condo). That's why we have insurance. Even this locking cabinet counts as a safe, with the beefed up locks and floor/wall mounting when coupled with my tweep-tweep stick-on "alarm" system.
With the barrio a mere 300 yards down the street, I want to keep firearms handy, yet secure when I'm away, and this fits my scenario for the moment. Total cost, $140 and a couple hours work and it will deter all but the most dedicated thieves.
ed