Free: Contests & Raffles.
Depending on the jurisdiction, and if I remember correctly, I'm pretty sure most residential floor joists are sized to provide at least 40 pounds per square foot (psf) of live load (stuff that can move) or 10 psf for dead load (stationary stuff). A 500 pound safe would need to cover 50 sq ft of floor, so I say stiffen it with a pad and some posts underneath.
I'm assuming you are going to put it next to the wall. I've never seen a gun safe in the middle of a room. So, you have nothing to worry about. The strength of the floor joist get higher the closer you get to an exterior wall, unless you have post and beam, then you probably have car-decking as well, and that is even better.I have a 12 gun safe, that I believe, weighs around 800 lbs. empty. I put it in the corner, and there is no worries on my part.
...2 guys standing are close to that load....