Honestly mate, at the 20$ budget, the best choice is the 7Hz Salnotes Zero, and it isn't even close. It comes very well tuned straight out the box and the build quality is very good especially at the price point. Much better build quality and tuning than the moondrop chu's imo. In fact, I use it over my DT770s, which are over a 150 quid more expensive.
There shouldn't be another iem you consider at this price.
Also, if you have a different budget, you can check out crinacle.com iem ranking, although the 7Hz zero isn't on there as he collaborated in making it and doesn't rank his own stuff because of bias
Tl;dr 7Hz zero at 20$, beats everything at that price range