I've done it a few times and the duty is of course based off the value of the drives. In my cases I've bought 1 or 2 drives at a time (20TB) and the duty was never more than $50, with about $10 of that being the processing fee.

Modern NOR flash has an expected lifespan of 10-40 years depending on the part. This is established using accelerated aging models. This assumes that no unaccounted-for design or manufacturing flaws arise in that time.