But that's not exactly a dollar cost average method if you waiting for the price to drop below certain threshold (in your case it's $50,000) and only buy then. So what let's say BTC goes down to 49k and you buy some with portion of your money, and then BTC goes back to 55k? Does that mean you won't buy again and instead you will wait for another "fair price"? How exactly is that DCA, and what if BTC never goes back below 50k, does that mean you won't buy ever again?

Point of dollar cost average method is to stop worrying about the current price and trying to time the market. Instead, you divide the money that you have to invest, and buy BTC in regular periods (let's say weekly or bi-weekly) no matter the price. In the long run this works flawlessly with bitcoin.