Generally speaking, there are three levels of safe marketed to gun owners.
1. The cheap ones from K-Mart and such. They're slightly more secure than a school locker, and will typically fasten with a Medeco key lock. They're aimed more at keeping inquisitive young hands off Papa's guns than at stopping a burglar. Weight is about 100 - 150 lbs at most. They' won't stop a determined teen who isn't concerned about damaging the safe.
2. The typical gun safe. S&G lock, weight 450+ lbs. Cannon, Browning, Ft. Knox, etc. fall into this category. Some exhibit better workmanship than others, but the bodies are typically 10 gage, meaning they'll stop a typical "smash & grab" robbery.
3. As #2, but with fire protection. Weight approximately doubles.
Talk to a real safe expert - the guy who supplies these (for example) to the jewelry trade, and he make take issue with calling any of these safes.
My advice . . . figure out the largest you'll need . . . and then go up at least a size. Maybe two; you WILL find things to fill it up with!