The good amount to buy bitcoin, i think $6,000-$7000 is good to buy bitcoin now. Because $6000-$7000 is low, compare to the price last year $19,000. For sure if you buy bitcoin now with that price and the price of bitcoin gets pump for sure you will gain huge profit.
If we can get a cheaper price than $ 6000 is certainly better, but if you look at the fact that happened in some time now it seems difficult to get the price of $ 6000, I'm sure May mei price soon reaches the range $ 10k- $ 13k, so buy with current price is a good price.