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I went the opposite route. I have a pair of nice earphones for my phone. They come with foamy inserts that you have to compress/roll up before inserting into your ear. Although they are not NRR rated, I'd venture to say that they provide about 20 db of protection. It doesn't matter too much anyway, since I always double up for safety, as I very much appreciate my hearing.

Now I found this microphone monitoring app for my phone. It has very low latency, so the audio delay is no problem whatsoever. It will take the audio input from the mic of my earphones, then relay it back to my ear at whatever volume I want. The built-in microphone compressor on the phone does a great job at attenuating very loud sounds. So if someone is talking at normal volume, I'd be able to hear it very well. But when there's a loud noise, it will drown it out like no one's business, just like the microphones used in those YouTube videos. The only downside of the app is that it requires the screen to be on the whole time. That's a limitation of the phone, though.

So I guess the point of the story is that I didn't spend a dime on electronic earphones. I just used what I had laying around.