I always find it interesting to compare 4TB/month pricing against buying N 4TB hard drives yourself, where N is the desired redundancy. Typically, you could buy a fresh set of hard drives 2-3x per year for the "standard" (they don't even call it "premium") storage tier. A normal drive lasts 5 years: go figure. (The markup was about double ten years ago, so it has gotten more competitive already.)
Of course, that's not entirely apples to apples because they save you labor time, but I find it an interesting baseline comparison, also because their labor is divided over a hundred thousand customers and approximates to zero per customer.
Another thing people tend to forget is that it's a backup copy, not your only. You don't need the premium storage if you keep the original copy around anyway and the odds of 3 unrelated drives (1 at home, 2 off-site) dying at the same time are probably better than you getting into a car crash this year. I did have 2 die at the same time: same make and model, nearly identical serial numbers, surprise: same crash date and crash behavior (few KB/s sequential read speeds for a while, but strangely no data was corrupted, before entirely crashing).