At $20.99, the current price sits 45% below the usual price of $37.99, a reference value calculated over 365 days. It is also the lowest price ever recorded: it has never been lower in the past year, and the period's high is $37.99.
The price is very stable, changing every 31 days on average. The realistically reachable low was $32.29, hit 2 times and held for 8 days in total. The current level is well below what was typically seen. The 90-day trend is downward (-18.9%), and 44 sales are estimated over that period.
This price is an all-time low, so buying now is reasonable. If you would rather wait, aim for $32.29 or less, a level seen before, but only for brief stretches. Given the roughly monthly pace of changes, a rebound is possible at the next shift.