The typical RSC type safe's that you see around for guns are a basic 12-18 ga steel box with a fancy door. While I will not go into how to get into one through either destructive or non-destructive methods, (there are plenty of videos out there unfortunatly to show the bad guys) my thoughts for you would be one of two things, or if possible both.
1. Find a place to either hide the safe or to disguise it to look like something else. It may be hard in some houses, but if they can not see it, or it doesnt screem valueables, it is a good chance it will be over looked by most.
2. Grab the yellow pages, and look for safe dealers and locksmiths. The commercial safe dealers will usually have used safes for sale, that are priced at 1/10 of the original price, and you get a rated safe as well. If you look around for a store closing or updating, you may get one for free if you haul it away.
3. (option as well) Whether or not you get a RSC or rated safe, I would think about putting one of these self contained alarm systems in to the safe. You can google it to get ideas, but enough noise to attract attention hopefully will help. Some also connect to your telephone line and have an autodialer that sends you a pre-recorded message, or you can connect it to your home alarm system as well.
You can look around and find Mosler, Diebold, etc type rated safes that are either free, come and get it, to as much as you want to pay. If you look and are patient, you may find one for 200-500 bucks which would be way better then most of the RSC type safes you find for sale.
True story.
If a determined thug wants what is in the safe, he will get it. We had a store that the thugs took an ax to the electrical service wires, then beat the built in wall/counter around a 2,000lbs safe, pried the safe off the floor, breaking the bolts holding it down, loaded it up, and took it with them. It was found day later opened up, and laying on the side of the road where they dumped it. Funny thing was, they attacked the loose VCR trying to get the tape out, and distroyed the VCR and the plastic cassette, but not the film inside, got the film out and put into another plastic cassette, and had a brief video before it went offline, but nothing that was 100% to ID the thugs. What I am trying to say is, if they want it, they will probably get it. Make it as difficult as possible, and do what you can to limit the time that they can be there to work at it.