The first question is do we want to buy during falling prices or during rising prices? The bitcoin price is very volatile right now and could be falling even lower in the next few weeks. But we shouldn't worry to much about what the price will be next week, rather what the price will be in 1 or 2 years. On that I think we can all agree that the price will be higher than it is today. Finding the bottom of a crypto coin is very hard. There are many factors to consider. In my opinion buying around the 30.000 USD level is a good idea. There are already quite a few high profile investors who stated they would heavily reinvest into bitcoins if prices drop to 20,000 USD. Waiting for the lowest possible price might lead to missing out on the next rally.