Bog, Jon is correct.If it says it will hold 24 guns,it will maybe hold 16 if you have optics on some of your guns.
Check with a local safe retailer,that's a high price for what is really a cheap gun safe.
A local safe co/locksmith might be able to get you into a much better/larger used safe for a better price.
The best safe that I ever had was given to me for free,I just had to get it moved.It was an old bank safe,and 2 grown men could stand inside it.
It took a 5 ton wrecker to lift it and bring it to my house,and I had to push it inside the garage with a tractor.It was still there when I moved,I couldn't put it in my new house.