Simply put, this is the established class-leader for cheap+good rds - Holosun Paralow HS403B 1x20mm 2 MOA Red Dot Sight

TL;DR This is THE affordable entry-level lightweight red dot. Start here.

It's the lower threshold of acceptable quality, features, and performance in a minimal form factor, IMO, yet it's a good value (especially on sale!).SO if you're on a tight budget, either get this or save until you can. Don't bother with anything less, and I say that not as a snob, but as someone who learned the hard way by incrementally climbing the quality ladder until the rungs quit breaking. If you start too low on the quality spectrum, you'll only end up wasting money as you inevitably upgrade beyond your $40-$70 RDS that won't hold zero. Just skip ahead to this unit if you want to do more than just dry fire at the far wall of your room and fantasize, mmmkay?. Even if it means you make do with irons for a while (Which is healthy, valuable learning time, anyway). You're not a poor, my friend, you're just being the best, sensible you that you can. Take you time and get there.

This is not a military-grade sight that can take an ongoing beating out in the field, but it's tough enough for range and HD use. Doesn't add much weight and the option to mount it at two different heights means you can use it on a variety of platforms, so it's a flexible investment. Low mount is great for anything from .22 plinking to shotgun to AK use. High mount is industry compatible for flat-top AR use, and co-witnesses with various BUISs nicely. Most importantly, the all-critical shake-awake feature takes this sight from mall-ninja fantasy land to usable defensive optic. In other words, when you need to pop back ASAP, you'll have an aiming point to do it with, instead of fumbling with your (Romeo MSR) knob being your last act on this earthly plane.