If theft is an issue then you will need to spend hundreds and preferably get one that you can bold to the foundation of your home.
If you are simply looking for a way to prevent your young son from getting into your guns then a
Sentinel or Stack-On cabinet will suffice and cost $120 to $150 new at Wally World. Yes, A thief will take a crowbar and pry it open in 20 seconds but in some cases that doesn't matter.
I bought a Sentinel ($100 off craigslist) and a Stack-On ($130 homedepot.com) for my closet. I just wanted to store my guns away from my grand children. If a thief cracks it open then fine, I'll already be dead because he will have already gained entrance into the house, into out bedroom, then past me and my 9mm I have hidden