The Gardall ES1612-G-E is definitely not what you want. It is just a fire safe and paying 125 bucks to bolt a fire safe down doesn't make sense.
Looking for a used safe is IMHO a good suggestion. People see safes often as a burden which they want to get rid. So they can be quite cheap. From what I have seen here I would not buy a a gun safe with "fire board" insulation. There might be good ones, but I believe most is crap. I would look for a certified fire protection and not just a self-declaration. Modern building don't have that much of a fire hazard anymore. Paper is also not so sensitive to heat. So I think a 1 hour rating should be very sufficient. I would look for a safe made by a company who can produce UL TL-rated safes even when you don't buy a TL-rated safe, just because the can apply their knowledge of the higher rated safes also to the lower rated ones. AMSEC is as suggested in this thread probably a good choice. When you have the safe, bolt it down as good as possible. Get it done by someone who knows how to do it and check his work. In Germany over 90% of all safes in private homes which are mentioned in police press releases are taken away for an opening. I am sure many are not bolted down at all, but there are also many which are not bolted down good enough.