I really don't see how it is all that easy to pry a gun safe door open. First I would think you would have to tip it over. And then pry enough to pop the bolts. Mine has 10 1" bolts around the door, and for a little more I could have got a gun safe with 12-15 1.5" bolts. So forgive me, I just don't see it being relatively quick, or quiet. Possible maybe, but not quick or quiet.
Let's assume that your safe has a 1/4" plate door with 1/4" bolt guides, and 1" bolts. Which is going to give way first?
A safe is only as strong as its weakest link. In this case, you could have 6" round door bolts, but the 1/4" door plate is still the weakest component. You could have 10 bolts, or 20 bolts, and the 1/4" plate would fail at the same rate.
When shopping for a safe, you have to look at what that weakest link is. The manufacturers will point out their strengths, but never their weakness.
You are correct in that the door is the strongest part of the safe in most cases.
For $5,000 I would expect at least quarter inch thick walls and a really heavy door.
For $5,000 you could get a much more secure safe. Think 1" steel plate walls with 1.5" steel plate doors. You won't find these types of safes in the same places gun safes are typically sold.
I find it absolutely incredible that someone with tends of thousands in NFA firearms stores them in a $100 safe which can be pryed open.
Any safe can be pryed open using the right equipment. Obviously, some easier than others.
I find it a bit hard to believe someone who is willing to invest $50K on a gun is not going to spend $400 or $500 to get a relatively good safe to keep it in. While a safe in this price range is not going to be as good as a $3000+ Fort Knox it would certainly be strong enough to make a smash n' grab burglar think twice about taking the time to attempt to open it.
In reality, there's not much of a difference between a $300 gun safe and a $3,000 gun safe. There is some, but not enough to justify the extra money.
If you are looking to protect from children and theives scared off by safes, then both the $300 gun safe and the $3,000 gun safe will provide the exact same level of protection.
If you are looking to keep somebody with tools out of your safe, you better have something made of substantial steel or composite construction.