I know that Prime Video has either rentals and purchase to own (regardless, the ones with higher resolution costs more when speaking about one time purchase rather than rentals). I’ve managed to purchase The Unit (All 4 Seasons) for about ¥4000 in total (or about ¥1000 per season in HD) on Prime Video (Japan). Rentals only last 48 hours while purchases are intended for lifetime streaming without an expiry date.
€, since I mentioned the currency in the sentence before that :)
Sure, ¥999 for a season sounds very nice but it all stays on Amazon’s servers. Whenever they feel like taking those down, I’d be extremely surprised if they first let you download the files to keep them. And correct me if I’m wrong but don’t you need a Prime subscription to access those digital purchases?