Most "gun safes" are actually:
"
RSC:
Residential Security Container. The minimum rating which should be used to protect assets from theft. This rating is usually not accepted for business use.
Ability to withstand 5 full minutes of rigorous prying, punching, chiseling, and tampering attacks by UL technicians with a hammer and screwdriver."
They are not safes as rated by Underwriters Laboratory.
The RSCs are 10 gauge steel or less, the door may be thicker.
The best gun safes are made by Graffunder and cost accordingly.
http://graffundersafes.com/
AMSEC makes a safe with 1/2" steel door and 1/4" sides with some fire insulation.
http://www.amsecusa.com/
If you are looking at $1,500 for a Fort Knox with 3/16" steel compare that to a $2,000 AMSEC.
Of course, your present investment in firearms may not justify an investment in this range.