As others said.
If any accuracy is needed, better industrial cutting wheels are available and can easily dress small cut size variations to very good hand-held accuracy around 0.1 mm or better.
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Tech below. Imho.
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My recommendation.
You can probably make a simple punch to finish the slot size very well.
A tapered punch in industrial O1 or air (oil) hardening drill rod.
Cut simple teeth with positive rake, 5-9 degrees goal, staggered left/right.
Aim for about 0.1 mm finish size vs plasma cut, or 5-10 teeth per set or side, or 10-20 teeth total.
Punch the thing through with any of your agri tools, using heavy cutting oil, and make a jig if necessary.
Make the jig about 100x heavier than you think you need.
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A jigged punch above might last 5-10-20 punches before getting dull.
5-10 mins with a hand-held spindle can sharpen it for another x runs.
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A custom tooth carbide cutter insert from a shop is not expensive.
They might cost about 10$ each, for simple ones like this, qty 40.
They could run 10x faster and make maybe 20-40x more pieces.
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If you need accurate slots, carbide burrs and simple jig supports can potentially get you to 0.02-0.04 mm in some terms of size, flatness, straightness, or position.
Or mounted points aka proper abrasives.
I mean it is quite easy to get a cut to be either,
flat, smooth, to size, or straight,
with cutting wheels and burrs and stuff. Fairly fast.
E.g.
1.
If You needed qty 1, very accurate slot it could be easily done with a NSK hand held spindle to about 0.02 mm accuracy, given metrology for same.
2.
Given some time and stuff, the slot could be 10x more volumetrically accurate, to about 0.002-0.004 mm over a slot.
This is about 2000x more difficult.
Or only 20x more difficult if some constraints are relaxed.
