I have several optics on my ARs:
- Aimpoint red dot
- Weaver 1-3x
- Zeiss 3-9x
I got the Weaver first as a general purpose optic and it was cheap at $150 or so. Works well at the range out to 200 yards for plinking. But the eye relief like any magnified optic is too limited (I felt) for self defense. And it is not enough magnification for sighting in handload tests. Much better than iron sights for my eyes but a compromise.
When I had more money saved I got two optics more specialized for different purposes. The Aimpoint is fantastic in terms of unlimited eye relief, rough eye position, and illuminated dot for quick target engagement out to at least 100 yds. The battery life is in terms of years. This is now my general purpose SD and plinker.
The Zeiss 3-9x is perfect for getting the utmost precision at 100 yd sight in targets, while still being able to double as a plinker or field gun at the lower magnifications.
I would plan to eventually get two optics: a Red dot for under 200 yd for defense, plinking, larger critters. And a variable up to 7x or more for precision work past 100 yds for targets, small varmints, etc.
Just figure out what you will use it for MOST and get that optic first. Sounds like SHTF might be a concern so the Aimpoint or EOTech would be better choice to start with. If you find the need for longer ranges later on then you can get another optic for that when you have the funds. I don't think you can ONE optic that does everything well and is battle hard proven for under $500. Don't scrimp on a defense optic and try to get a bunch of cheaper gadgetry to cobble together a compromise. Focus on the primary need and get the best you can afford for that purpose.
Even within the magnified variable scopes you need to decide your purposes in order to get the best suited reticle: heavy, thin, turret BDC or reticle ranging dots, illuminated or not, etc. Only get features you know you need and how they are better than other options. The last thing you want is an optic that you spend too much time trying to figure out for simple everyday use.
"The ultimate authority ... resides in the people alone. ... The advantage of being armed, which the Americans possess over the people of almost every other nation ... forms a barrier against the enterprises of ambition."
- James Madison