A budget loadout does not start with a “budget” rifle. I strongly recommend against picking low quality carbines for anything other than a plinker/tester/fun rifle. Parts QC is simply not high enough. Save and buy a quality gun.
Using a 10.5″ AR Pistol as our base will usually require the addition of iron sights, certain models may come with a set. The beloved budget friendly standard are MBUS Gen 2’s from Magpul.
The iron sights are the emergency sight option. A Red Dot Sight (RDS) is your primary sight and takes care of both good light and low light/no light aiming.
A good RDS simplifies aiming. The best RDS systems are durable enough that some users are omitting back up sights entirely. I still run backup irons, and will for the foreseeable future. The Romeo 5 on this 2A Balios can be found for around $119.
The light system remains. The budget spent is still about what was spent on the minimalist light. The light needs to reliably come on when you ask it too, function under recoil, and illuminate the effective envelope you need. That’s all. My preference on a budget is the TLR-7.
Stock trigger, don’t need to spend there. A stock safety, again not a necessary spend for an upgrade. I did swap the pistol grip to a BCM and added a QD sling point. Less than $40 invested.
Total ancillary add on was under $400.