I was sort of in your situation a couple years ago.
At the time, my wife and I were renting and I decided I needed a safe. Unlike you, I did no seek the thoughts of arfcom prior, and bought what I thought was a great/secure safe. I bought a Liberty Franklin 24 for about $1,600. (maybe 27 gun, can't quite remember). After a couple months, I learned that what I had was a Residential Security Container, not a true "Safe". The Franklin did have some upgraded features like slightly thicker steel, a higher fire rating, and more/thicker bolts than the lower models, but, it still wasn't a true "Safe". I too, was unable to bolt it to the floor as we were renting.
Fast forward to today, and it is in the house we own, bolted to the wall and the basement floor. It has become full, so full that I can't store ammo in it any longer. I'll soon be in the market for a real safe such as a Sturdy and relegate the Liberty to storing ammo - my finances just aren't there yet.
When we were renting, we were in a low-crime neighborhood, in a high-crime region (St. Louis). Now, I live in an EXTREMELY low crime area. Break-ins ALWAYS make newspaper headlines around here... generally front page.
I'm of the opinion that the RSC Liberty will suffice for the quick smash and grabs... especially when I have neighbors who know me, some that are home all day every day, and we communicate with one another regularly. I have no illusions that my Liberty would hold up to more than about 10 minutes if a perp came in with some basic tools and a plan to specifically get at the guns. However, that would involve perps knowing in advance where the safe is, what is in the safe, an opportunity to do it, etc. Personal security is probably the most important aspect in my life with regards to keeping my guns secure. I don't talk about any of my weapons, except with family or very close friends that I also shoot with.
Truth be told, a determined thief will get your goods regardless of what kind of safe you have - RSC or something substantial like a Sturdy. If they can get access, have the tools, the opportunity, the motivation, and plenty of time, they'll get them.
In your situation, especially as you want to spend $1,500 or less, I'd look at finding an RSC with 11ga steel, thicker bolts, and a good mechanical lock. That may not get you to a 50ish gun safe, but it'll get you a decent level of protection from smash and grabs. If you find, after building your home, that you need more space, you could look at selling your RSC and upgrade, or add another real safe.