So, I bolded your usage plans above to highlight what they mean to me in terms of optic selection, below...

Plinking = generally larger targets, meaning lower demand for accuracy, slow to moderate fire at short to moderate range, often firing not supported. Optic Selection: lower price, mid-range to low range magnification.

Ringing Steel = larger targets for a given range, meaning less demand for accuracy, slow to moderate fire rate, typically supported or prone fire. Optic Selection: Mid-range magnification.

200 Meters = relatively short range, but long enough to generally require supported shooting position. Parallax issue is less critical/prevalent. Optic Selection: Mid-range magnification, doesn't necessarily need parallax correction.

So...

If I tally that up:

1) I'd advise against iron sights or a solo red dot sight - the precision just isn't there. An 8" steel gong at 200m is only ~4MOA, which means a normal red dot will nearly fully cover the target = not good for reliable hits. The front sight in iron sights typically covers about 10MOA with 2-5MOA drift for the front sight in the rear sight, so similarly, drifting by a few MOA with irons is very easy.

2) The exception to the above is a magnified red dot sight, or a red dot sight with an added magnifier. Probably not gonna get many of these in the $400 or less ballpark, however.

3) A mid-range variable zoom scope would be my recommendation. Pick up a Bushnell Elite, Nikon Prostaff, or Leupold VX-2 3-9x40mm and you'll be fine. No need to spend extra for parallax adjustment, no need to go any higher than 3-9x or 3.5-10x, maybe 4-12x if you want. Even a fixed 4x would be fine for banging steel at 200yrds.

Most of my AR's have different applications from your own, so what I have on mine probably isn't very relevant for you. I have short range shooters with iron sights and/or red dots and I have magnified red dots on longer range shooters, but most of my AR's have scopes on top. But I'm not generally very satisfied with hitting a 2-4MOA steel gong - I'd much rather put a sub-moa group in the middle of a gong or paper target - so I put a little more optic on top of mine. I also do most of my shooting well past 200yrds, so my optic has to be versatile enough to reach mid to long range without inducing parallax errors.

I do have 2 AR's right now with what I'd say are suitable for what you're needing, even though the optics are a lot cheaper than you're looking at (and they're not good scopes either). One wears a 3-9x40mm Bushnell AR, junk scope, but it was only $150 and I needed a temporary scope for this upper. The other wears a Nikon Buckmaster 4-12x40mm, also not great, but also only $150 when I bought it and only a temporary solution, since I shoot this one most often at night with a red-dot sight. My other AR's wear red dots (trijicon RMR, Burris FastFire, Eotech 512), iron sights, or higher magnification scopes like 2.5-16x50mm, 4.5-14x50, 6-18x40, 6-24x44, 4.5-30x50mm, etc all of which have adjustable objectives or side focus, and most of which cost a lot more than $400.