I agree that a large crowbar or sawzall will defeat most RSCs very quickly. If you look on craigslist/offer up/marketplace for a used safe you can find some real bargains. Look for a UL rating of TL-15 or TL-30 (the safe will have a nameplate saying what it was tested to) and you'll be getting a safe that actually earns the name "safe". An older TL-15 will have a door that is 1/2" steel, with the same age TL-30 being an inch thick. Newer TL-15 or TL-30 will be steel wrapped around concrete, with nasty stuff like carbide embedded in the concrete to kill drills and saw blades.
TL-15 and TL-30 are test specifications done for tests at UL. They specify what tools can be used, how long, etc. There is an old but interesting test here:
The biggest issue with a TL-15 or TL-30 safe is going to be the weight and getting it where you want it. After that you're good to go.