Basically, there are several methods for trading Bitcoin, as is often done by many crypto users, for example: spot trading, Margin, Futures, these three methods are often used by most users, As far as I know, these three methods are carried out based on the current price of Bitcoin and so on, you could say it depends on the market situation.
So, it's hard to say the first Bitcoin price to trade, maybe I don't remember what price I started from, but overall I did it when Bitcoin was going down, It's up to you what the price is, but stick to market guidelines, charts, analysis, volume and so on.
For trading Bitcoin, it is not so important what the price was when you started trading, if it is day trading, or medium-term trading, then the price will be constantly different, and you will need to act according to the situation. And if you buy bitcoin for long-term transactions, then in this case the price will be of great importance, but everything regarding long-term transactions, from a year or more, I personally consider investing, it’s easier for me. In this case, you should calculate the average purchase price that you will get, this will be your purchase price.