Just because a coins is low in price doesn't mean it's the perfect opportunity for buying and just because a coin is high in value shoudn't discourage you from purchasing it. What matters most in the industry is the supply of a project (preferably the circulating supply). As you can see with Bitcoin, Bitcoin only has 21 million coins that can ever exist and enter the market so it doesn't matter if it's been priced at $100k or above, it's still cheap as the price is designed to keep on appreciating as the demand increases.

Also buying a coin that is down can be very danger especially when they aren't Bitcoin as there's no guarantee of the coin recovering with the general market which is why people tend to wait for the trend to turn bullish then fomo into the market. Nobody would want to but at the highs, everyone you see will always want to get the coins at their bottoms but with cryptocurency, you can never be too sure which price is the bottom therefore the best advice for investing has always been to dollar cost average instead of investing one time.